Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper or lightly grease it.
In a large bowl, combine the sliced bell peppers and onion. Drizzle with 1 tablespoon of olive oil, then sprinkle with salt, pepper, and 1 teaspoon of fajita seasoning. Toss until the vegetables are evenly coated.
On the prepared sheet pan, spread the seasoned vegetables out into an even layer in the center of the pan, leaving space on the sides for the salmon fillets.
Place the salmon fillets on the sheet pan, skin-side down. Drizzle with the remaining tablespoon of olive oil, lime juice, and sprinkle the remaining teaspoon of fajita seasoning on top. Season with salt and pepper.
Bake in the preheated oven for about 15-20 minutes, or until the salmon is cooked through and flakes easily with a fork, and the vegetables are tender and slightly charred.
Remove from the oven and let it cool for a few minutes. Garnish with freshly chopped cilantro before serving.
Serve the fajita salmon and vegetables with warm tortillas for a complete meal.