Cheesy Pub Burgers with Griddled Onion, Chipotle Sauce, & Potato Rounds

Adjust rack to top position and preheat oven to 450 degrees. Wash and dry produce. Slice potatoes into ¼-inch-thick rounds. Toss on a baking sheet with a large drizzle of oil, half the garlic powder, salt, and pepper. Roast on top rack until lightly browned and tender, 20-25 minutes.