Melt the butter. Preheat oven to 400°F. In a saucepan, melt butter over medium. Prep the salmon. Place salmon, skin side down, on one side of a baking sheet. Add asparagus to the other side of the baking sheet. Drizzle melted butter over salmon and asparagus; sprinkle with salt and pepper. Bake 12 to 15 minutes or until salmon is cooked through and flakes easily with a fork, and asparagus is tender. Make the topping. In a small bowl, combine mayonnaise, green onion, parsley, lemon peel, and lemon juice. Serve with roasted salmon and asparagus. If desired, top with additional parsley.