Preheat oven to 350 degrees F (180 degrees C). Line a rimmed 9x12-inch baking sheet with parchment paper and grease with cooking spray. Place salmon fillets and asparagus in a single layer.
Combine olive oil, lemon juice, and garlic in a bowl. Drizzle garlic mixture over salmon and asparagus. Season with salt and pepper. Place lemon rounds on top.
Bake in the preheated oven until salmon flakes easily with a fork, 15 to 20 minutes.