Adjust rack to top and bottom positions and preheat oven to 425 degrees. Wash and dry all produce. Cut potatoes into 1/2-inch-thick wedges. Halve, peel, and very thinly slice onion. Pick 1 tsp thyme leaves (2 tsp for 4 servings) from sprigs; reserve remaining sprigs for step 2. Cut tomato into 8 wedges (16 for 4). Halve lemon.

Heat a large drizzle of olive oil in a large pan over medium-high heat. Add onion and thyme sprigs; cook, stirring occasionally, until browned and softened, 10-15 minutes. (TIP: Lower heat and add a splash of water if onion starts to burn.) Discard sprigs; add half the stock concentrates, 1 TBSP sugar, and 1 TBSP butter (2 TBSP of each for 4). Season with salt and pepper. Turn off heat. Transfer to a small bowl; cover to keep warm.

Meanwhile, toss potatoes on a baking sheet with a large drizzle of olive oil, half the Fry Seasoning, salt, and pepper. Roast on top rack, flipping halfway through, until golden brown and tender, 20-25 minutes. Line a second baking sheet with foil; place bacon on sheet. Roast on bottom rack until crispy, 12-15 minutes. Transfer to a paper-towel-lined plate.

Cut top off carton of cream sauce to open fully; pour contents into a medium microwave-safe bowl. Using a spoon or spatula, scrape any remaining sauce from carton into bowl. Add remaining stock concentrates; stir to combine. Microwave until steaming, 1 minute. Whisk in mozzarella and thyme leaves until smooth and slightly thickened. Season generously with salt and pepper. Microwave another 30 seconds, then stir again.

In a second medium bowl, combine beef and remaining Fry Seasoning. Form into two patties (four patties for 4 servings), each slightly wider than a burger bun. Season generously all over with salt and pepper. Heat a drizzle of oil in pan used for onion over medium-high heat. Add patties and cook to desired doneness, 3-5 minutes per side. Halve buns; toast until golden.

In a large bowl, toss mixed greens and tomato with a large drizzle of olive oil and lemon juice to taste. Season with salt and pepper. Microwave sauce again until warmed, 30 seconds; whisk in 1 TBSP butter (2 TBSP for 4). Fill buns with patties, caramelized onion, bacon, and some sauce. Serve with salad, potato wedges, and remaining sauce for dipping on the side.