Heat cast-iron skillet or grill pan over medium-high. Brush flesh of orange, lime, and pepper with oil. Once pan is hot, place orange and lime in pan, cut sides down. Gently press down on fruit with spatula. Cook until flesh begins to char, approximately 2 to 3 minutes, then remove lime and flip oranges to char the other cut side. Add pepper to pan and heat until blistered in a few places.

Peel rind off charred orange slices, then place into food processor. Squeeze juice from charred lime into food processor. Slice jalapeno or serrano pepper and remove seeds; add to food processor along with red onion, cilantro, mint, garlic, and salt. Pulse until a finely chopped consistency is reached.

Heat oven to 325 F. Line baking sheet with parchment paper.

Place salmon on prepared baking sheet and season with salt and pepper. Bake salmon in preheated oven for 16 minutes, or until just barely cooked through in centre.

Serve salmon topped with orange salsa.