Grease a large baking pan. Arrange salmon and asparagus on the baking pan. Scatter the onions on top of salmon and asparagus. Drizzle olive oil, season fish with garlic salt, dill, black pepper and drizzle butter over fish.
Bake for 25 to 30 minutes or until done. Serve with lemon.
Recipe by The Gluten Free at https://www.theglutenfree.com/gluten-free-baked-salmon-and-asparagus/