1. Preheat oven to 425 degrees Fahrenheit or preheat a grill pan/grill over medium heat.
2. Oven: Prepare a sheet pan with parchment paper or nonstick spray. Toss onion, bell peppers and salmon with a drizzle of olive oil, kosher salt, and black pepper to taste, and any additional spices you like. Arrange in an even layer on the sheet pan and roast for 25 to 30 minutes.
3. Grill: Drizzle salmon with olive oil, season with kosher salt and black pepper to taste and any additional spices you like. Arrange on the grill pan and cook five to seven minutes depending on the thickness of your filets. Flip and cook until done to your liking, then transfer to a plate or platter and set aside to rest. Repeat with onion and bell pepper while the salmon rests.
4. Sprinkle with chopped cilantro and serve with limes.