To a large 18 x 26-inch baking sheet, add your prepared mushrooms and asparagus. Add the olive oil, salt, and pepper, and toss to coat. If you're adding any optional toppings, add them now, too (except for Parmesan cheese or finishing oil—add those at the end!). Then, spread the vegetables out in a single layer.
2 tablespoons extra-virgin olive oil, ½ teaspoon salt, ¼ teaspoon ground black pepper, 2 teaspoons lemon juice, 2 cloves garlic, minced, ½ teaspoon garlic or onion powder, ¼ teaspoon crushed red pepper, 2 tablespoons butter