Heat the oven to 220 C / 430 F. Take the lamb racks out of the fridge 20 minutes before cooking and pat them completely dry with paper towels.

Season the lamb generously on all sides with salt and black pepper.

Combine the breadcrumbs, rosemary, thyme, parsley, garlic, olive oil, salt, and pepper in a small bowl. Stir until the breadcrumbs are evenly coated in oil and the herbs are well distributed.

Heat 1 tbsp olive oil in a 10-inch oven-safe cast iron skillet over high heat until the oil just begins to smoke.

Place the lamb racks fat-side down in the skillet. Sear for 2 to 3 minutes until deep golden brown, then sear the other sides briefly, about 1 minute each, to build color.

Remove the skillet from the heat. Transfer the lamb racks to a wire rack set over a baking sheet, bone-side down.

Brush the fat side of each rack with 1 tbsp of Dijon mustard, covering the top and sides evenly.

Press the herb breadcrumb mixture firmly onto the mustard-coated surface of each rack, creating an even layer.

Roast in the preheated oven for 18 to 20 minutes, until the crust is deep golden and an instant-read thermometer inserted into the thickest part reads 57 C / 135 F for medium-rare.

Transfer the racks to a cutting board and rest for 8 minutes without cutting.

While the lamb rests, heat 1 tbsp olive oil in the same cast iron skillet over medium heat. Add the sliced garlic and cook for 30 seconds until fragrant but not browned.

Add the spinach or chard and toss with tongs for 1 to 2 minutes until wilted and bright green.

Add the lemon juice, salt, and a pinch of red pepper flakes if using. Toss once more and remove from heat.

Slice between the bones to separate the rack into individual chops. Arrange 2 to 3 chops per plate alongside a portion of the wilted greens. Spoon any pan juices over the lamb before serving.