1
Adjust rack to top position and preheat oven to 425 degrees. Wash and dry all produce.
Cut potatoes into ½-inch-thick wedges. Trim and thinly slice mushrooms. Halve, peel, and thinly slice onion.
In a small bowl, combine mayonnaise with ¼ tsp garlic powder (½ tsp for 4 servings); season with salt and pepper. (You’ll use the rest of the garlic powder in the next step.)