Preheat oven to 400°.
Snap off tough ends of asparagus; remove scales with a knife or vegetable peeler, if desired. Set aside.
Rub cut sides of garlic over a 13 x 9-inch baking dish; place garlic in dish. Add asparagus; drizzle with oil. Sprinkle asparagus with salt, thyme, and pepper; toss gently. Bake at 400° for 20 minutes, stirring once.