1Heat oven to 400º. Spray rectangular baking dish, 13x9x2 inches, with cooking spray. Sprinkle asparagus, onions, 1 1/2 cups of the cheese and the salmon in baking dish.
2Stir remaining ingredients except cheese until blended. Pour into baking dish.
3Bake 40 to 45 minutes or until knife inserted in center comes out clean. Sprinkle with remaining 1 1/2 cups cheese. Bake about 2 minutes or until cheese is melted. Cool 5 minutes before cutting.