Preheat the oven to 350 degrees F (175 degrees C). Lightly coat a large baking sheet with cooking spray.
Snip the white ends off of the asparagus so that all of the stalks are roughly the same length. Lay the stalks on a baking sheet so that they are all touching.
Drizzle asparagus stalks with olive oil. Shake the onion soup mix packet to mix up any settled ingredients; sprinkle over asparagus.
Bake in the preheated oven until softened and lightly browned, 25 to 35 minutes.
Remove from oven; sprinkle mozzarella cheese on top of the asparagus. Continue baking until cheese is melted and starting to brown, about 5 minutes more.