Combine the thinly sliced red onion with 2 tbsp lime juice and a pinch of salt in a small bowl. Toss well and set aside for at least 10 minutes while you prepare the mushrooms. The onion will soften and turn bright pink.

Heat the oven to 220 C / 425 F. Line a large rimmed sheet pan with parchment paper.

In a large mixing bowl, whisk together the minced chipotle, smoked paprika, cumin, garlic powder, oregano, orange juice, olive oil, soy sauce, salt, and black pepper until combined.

Add the torn oyster mushroom strips to the bowl and toss well until every piece is coated in the spice mixture.

Spread the mushrooms in a single layer on the prepared sheet pan. Do not overlap them. Use two pans if needed.

Roast for 15 minutes until the mushrooms are starting to shrink and dry out, then increase the oven to 230 C / 450 F and roast for a further 8 to 10 minutes until the edges are caramelized and slightly crispy.

Heat a dry cast iron skillet over high heat. Add the roasted mushrooms in a single layer and cook for 2 to 3 minutes without stirring until the edges crisp up further. Work in batches if needed.

Warm the corn tortillas directly over a gas flame for about 20 seconds per side until lightly charred, or in a dry skillet for 30 seconds per side.

Pile the mushroom carnitas onto warm tortillas. Top with pickled red onion, sliced avocado, and fresh cilantro. Crumble cotija cheese over the top if using. Serve with lime wedges.