Preheat your oven to 375℉. Line a baking sheet with parchment paper. Place the salmon, skin side down, in the middle of the baking sheet. Place the tomatillos, onion rings, chile halves, and garlic around the salmon in a single layer. Season everything on that baking sheet with salt and pepper to taste, then drizzle olive oil over top of everything. Place the lime slices on top of the salmon.
Roast for 20 minutes for rare. Transfer the salmon to a serving platter. Return the baking sheet with the veggies to the oven and roast for another 15 minutes.
Carefully scrape the veggies into your food processor. Add the handful of cilantro plus the juice of 1 lime. Process until smooth but still a little chunky. You’re making salsa, so you want salsa texture. Taste for seasoning and add more salt if necessary. Pulse it in so you don’t wreck your salsa texture.
To serve, transfer the salsa to a serving bowl. I like to plate up family style. We use forks to dive into the salmon and chunk it up into the tortillas. Then spoon salsa over, and garnish with chopped raw onion and a little more cilantro, plus the lime wedges for squeezing over.