Adjust rack to top position and preheat oven to 450 degrees. Wash and dry produce. Slice potatoes into 1/4-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.

Meanwhile, peel and cut onion into two 1/4-inch-thick rounds (four rounds for 4 servings), keeping layers intact. Halve buns. Thinly slice half the pickle into rounds; cut remaining half into spears.

In a small bowl, combine mayonnaise, sour cream, remaining garlic powder, and chipotle powder to taste. (Start with a pinch, then taste and add more chipotle powder from there if desired.) Season with salt and pepper.

Heat a drizzle of oil in a large pan over medium-high heat. Add onion and cook until tender and browned at the edges, 2-4 minutes per side. Season with salt and pepper. Transfer to a plate.

Meanwhile, form beef into two patties (four patties for 4 servings), each slightly wider than a burger bun. Season generously with salt and pepper. When onion is done, heat a drizzle of oil in same pan over medium-high heat. Add patties and cook to desired doneness, 3-5 minutes per side. In the last 1-2 minutes of cooking, top each patty with gouda; cover pan until cheese melts, 1-2 minutes.

While patties cook, toast buns until golden brown; spread with a layer of sauce. Fill buns with patties, sliced pickle, and griddled onion. Serve with potatoes, remaining sauce, and pickle spears on the side.