Preheat oven to 450 degrees.
Line a baking dish with foil and spray with cooking spray.
Place sliced onions in a single layer on the bottom of the prepared dish.
Top onions with pineapple rings.
Lay salmon on top of pineapple. Sprinkle salmon with salt and pepper.
Generously brush salmon with barbecue sauce.
Cover and bake for approximately 6-7 minutes. Remove cover and bake for an additional 6-7 minutes, or until fish flakes easily with a fork. Don’t over-cook the fish or it will be dry.