Preheat oven to 450° F. Place
asparagus spears and mushrooms on a large baking sheet. Drizzle oil and sprinkle
rosemary over asparagus and mushrooms. Gently toss to evenly coat.
Arrange asparagus and mushrooms in
a single layer on the baking sheet. Season with pepper and, if desired, garlic powder.
Bake 10 to 15 minutes, or until asparagus is tender-crisp.