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Oily fish traybake with fennel is a one-pan dinner for four: salmon fillets roasted alongside fennel wedges and baby potatoes at 200 C / 400 F. It takes 54 minutes, and about 15 of those are hands-on.
I’ll be honest. Fennel was the vegetable I walked past for years. Raw, the aniseed bite is loud. Roasted, it turns soft and lightly sweet, with browned edges that taste almost nutty.
The vegetables go in first so they actually brown. The fish joins them for the last 14 minutes, which keeps the salmon juicy instead of chalky. Lemon and capers cut through the richness.
One pan. Real food doing its thing. And it sits right in a weeknight rotation.
Why You’ll Love This Recipe
- One sheet pan means almost no washing up.
- Salmon gives you protein and omega-3 fats in one go.
- Fennel turns sweet and mellow once it’s roasted.
- Prep is 15 minutes, and the oven does the rest.
Ingredient Notes
- Salmon fillets: Buy skin-on fillets about 3 cm thick so they cook evenly in 14 minutes. Trout works the same way. Mackerel is thinner and spoils faster, so buy it the day you cook it and keep it cold.
- Fennel bulbs: Choose firm, white bulbs with fresh green fronds. Trim the tough stalks and save the fronds for garnish. Sliced onion wedges are a weaker substitute, but they’ll do in a pinch.
- Baby potatoes: Quarter them to about 2 cm so they finish at the same time as the fennel. Yellow-fleshed new potatoes hold their shape best.
- Capers: Drain them well and don’t add extra salt on top. They go in with the fish and soften slightly in the heat. Chopped green olives are a fair swap.
- Fennel seeds: A light crush with the flat of a knife releases the aroma. They double down on the aniseed flavor, so skip them if you’re still warming up to fennel.
Easy Roasted Oily Fish Traybake with Fennel and Potatoes
Ingredients
Method
- Heat the oven to 200 C / 400 F. Cut each fennel bulb into 8 wedges through the core so the layers stay together, and chop the fronds for later. Quarter the potatoes to about 2 cm and cut the red onion into 6 wedges.
- Toss the fennel, potatoes, onion, garlic and fennel seeds in a large bowl with 2 tbsp olive oil, 3/4 tsp salt and the pepper. Spread everything on a 33 x 46 cm / 13 x 18-inch rimmed sheet pan in a single layer with space between the pieces, cut sides down.
- Roast for 25 minutes, turning the vegetables once at the 15-minute mark, until the fennel edges are browned and a knife slides easily into a potato.
- While the vegetables roast, pat the salmon dry. Rub the fillets with the remaining 1 tbsp olive oil, 1/2 tsp salt and the lemon zest.
- Pull the pan out and push the vegetables to the edges to make four gaps. Set the fillets skin side down in the gaps and scatter the capers and lemon slices over the vegetables.
- Roast for 14 minutes, until the salmon is opaque, flakes easily, and reads 145 F / 63 C at the thickest part.
- Squeeze the reserved lemon half over the pan and scatter the fennel fronds and parsley on top. Serve straight from the pan.
Notes
- Quarter potatoes to about 2 cm so they cook through in 25 minutes.
- Cut fennel wedges through the core so the layers hold together.
- Pat the salmon dry before oiling for crisper skin.
- Pull the pan once the thickest part of the fish reads 145 F / 63 C.
- Save the fennel fronds and chop them over the top before serving.
Tips for Success
- Cut fennel wedges through the core so the layers stay attached and don’t fall apart on the pan.
- Spread the vegetables in a single layer with gaps between pieces, and use two pans if yours is smaller than 33 x 46 cm.
- Pat the salmon dry with paper towels before oiling so the skin crisps instead of steaming.
- Check the thickest part of a fillet with an instant-read thermometer at 12 minutes, and pull the pan at 145 F / 63 C.
- Chop the saved fennel fronds like dill and scatter them over the top for a fresh finish.
Variations
- Swap the salmon for trout fillets of similar thickness, or use mackerel fillets and start checking them at 10 minutes.
- Replace the potatoes with 400 g of 2 cm butternut squash or carrot pieces. The roasting time stays the same.
- Whisk 1 tbsp wholegrain mustard into the olive oil you rub on the fish for a tangy crust.
Storage and Reheating
Roasted oily fish traybake with fennel is best eaten fresh. Salmon turns dry and chalky when it goes back into the heat, and the potatoes lose their crisp edges.
Leftovers keep in an airtight container in the fridge for up to 3 days. Eat them cold or at room temperature. Flake the salmon over a green salad or into a sandwich, with the fennel and potatoes on the side.
For a make-ahead plan, do the cutting, not the cooking. Quarter the potatoes and hold them in cold water in the fridge for up to 24 hours, then drain and dry them well. Wedge the fennel and store it in an airtight container for the same time. Freezing doesn’t work here, because fennel and potatoes go mushy after thawing.
Serving Suggestions
Serve the traybake straight from the pan with the lemon half alongside. Spoon the browned bits and pan juices over the potatoes.
A peppery arugula salad with a mustard and lemon dressing is all it needs. Crusty bread is good for mopping up the juices. A spoon of plain yogurt with dill suits the fish if dairy is fine for your table.
Kids tend to go for the potatoes first. Flake the salmon off the skin for them and let them come around to the fennel on their own.
FAQ
How do I know when the salmon in an oily fish traybake is done?
The salmon is done when the flesh turns opaque and flakes easily at the thickest part, and an instant-read thermometer reads 145 F / 63 C. For 3 cm thick fillets that takes about 14 minutes at 200 C / 400 F. If white protein beads up on the surface, it’s close to overdone.
Can I use mackerel instead of salmon in a fish traybake with fennel?
Yes. Use four skin-on mackerel fillets of about 120 g each and start checking at 10 minutes, since they’re thinner than salmon. Mackerel spoils faster, so buy it the day you cook it and keep it cold. Its stronger flavor works well with the lemon and capers.
Why is my roasted fennel pale and soft instead of browned?
Crowding is almost always the cause. Packed pieces steam each other instead of roasting. Spread the vegetables in one layer on a 33 x 46 cm / 13 x 18-inch pan with gaps between pieces, set the cut sides down, and use two pans if yours is smaller. Wet fennel steams too, so dry it well.
Can I prep the salmon and fennel traybake ahead or freeze it?
Prep ahead, but cook it fresh. Wedge the fennel and quarter the potatoes up to 24 hours ahead and keep them cold. Don’t freeze the cooked traybake, because the fennel and potatoes turn mushy once thawed and the salmon dries out. Leftovers keep 3 days in the fridge and are best eaten cold.
What goes well with a salmon and fennel traybake?
Because the potatoes are already on the pan, keep the sides light. A peppery arugula salad with a lemon and mustard dressing works well, as does crusty bread for the pan juices. A spoon of yogurt with dill suits the fish if you eat dairy.
Is this oily fish traybake gluten free and dairy free?
Yes, as written it’s both. There’s no flour, butter, or cheese, just fish, vegetables, olive oil, lemon, and capers. If you’re strictly gluten free, check the labels on the capers and on any mustard you add. Skip the yogurt topping to keep it dairy free.
