Adjust rack to top position (top and middle positions for 4 servings) and preheat oven to 425 degrees. Wash and dry produce. 

Heat a medium dry pan over medium heat. Add bacon*; cook, turning occasionally and adjusting heat if browning too quickly, until crispy, 6-10 minutes.

Turn off heat; transfer to a paper-towel-lined plate to cool. Wipe out pan.

Meanwhile, trim, peel, and halve carrots lengthwise; cut into ¼-inch-thick half-moons. Halve and peel onion; thinly slice one half. Cut remaining onion half into ½-inch-thick wedges (thinly slice one onion and cut the other into wedges for 4). Halve peach and remove pit; cut into ¼-inch-thick slices. Halve buns.

Toss carrots on one side of a baking sheet with a drizzle of oil, salt, and pepper. Toss onion wedges on empty side with drizzle of oil, salt, and pepper. (For 4 servings, divide between two sheets; roast carrots on top rack and onions on middle rack.)

Roast on top rack until lightly browned and tender, 12-15 minutes.

Meanwhile, melt 1 TBSP butter (2 TBSP for 4 servings) in pan used for bacon over medium-high heat. Add peach; cook, stirring occasionally, until softened, 8-10 minutes. Reduce heat to medium; add peach jam, 2 TBSP water, ½ tsp sugar, and ¼ tsp salt (4 TBSP water, 1 tsp sugar, and ½ tsp salt for 4).

Turn off heat. Continue to stir until mixture begins to thicken and most of the liquid has evaporated, 2-3 minutes more.

In a medium microwave-safe bowl, combine sliced onion, half the balsamic vinegar, 2 TBSP water, ½ tsp sugar, and ¼ tsp salt (4 TBSP water, 1 tsp sugar, and ½ tsp salt for 4 servings). Cover with plastic wrap; microwave 30-45 seconds. Transfer pickled onion to a large bowl, leaving pickling liquid in the medium bowl; reserve.

Form beef* into two patties (four patties for 4 servings), each slightly wider than a burger bun. Season all over with salt and pepper.

Heat a drizzle of oil in a large pan over medium-high heat. Add patties and cook until browned, 3-5 minutes per side.

In the last 1-2 minutes of cooking, top each patty with gouda; cover pan until cheese melts and patties reach desired doneness.

While patties cook, add mustard, 2 TBSP olive oil (4 TBSP for 4 servings), a pinch of salt, and pepper to bowl with reserved pickling liquid; whisk to combine.

In a small bowl, combine BBQ sauce and remaining balsamic vinegar.

Toast buns, cut sides down, directly on top rack. Toast until golden brown, 2-3 minutes.

To bowl with pickled onion, add arugula, almonds, carrots, and balsamic dressing; toss to combine.

Spread cut sides of bottom buns with half the BBQ sauce. Fill buns with patties, bacon, caramelized peach, and as much roasted onion as you like. Drizzle with as much remaining BBQ sauce as you like. Divide burgers and salad between plates and serve.