Oven-Roasted Asparagus and Mushrooms... 1 bunch Asparagus 1/2 package White Mushrooms Olive Oil Salt, Pepper, and Garlic Powder... Wash and chop asparagus into 1" pieces. Slice mushrooms. Add both vegetables to a baking dish. Lightly coat with olive oil, mixing to ensure that everything is evenly coated. Sprinkle with salt, pepper, and garlic powder. Roast at 400F for approximately 30 minutes, to desired tenderness.