Wash and dry all produce. Preheat oven or toaster oven to 400 degrees. Halve, peel, and thinly slice onion. Heat a large drizzle of olive oil in a large pan over medium heat. Add onion and 2 tsp sugar. Cook, tossing, until browned, 6-8 minutes. Season with salt and pepper.

While onion cooks, mince or grate garlic until you have 1/2 tsp. In a large bowl, whisk together 1 TBSP tomato paste, 2 TBSP balsamic vinegar, 2 TBSP olive oil, and as much minced garlic as you like (we sent more tomato paste and vinegar than needed). Season with salt and pepper

Wipe out same pan, then heat a large drizzle of olive oil in it over medium-high heat. Shape beef into 4 patties. Season all over with salt and pepper. Add to pan and cook until just shy of desired doneness, 2-4 minutes per side. Sprinkle mozzarella on top of each. Cover pan and continue cooking until cheese melts, about 1 minute more.

While burgers cook, split ciabattas in half. Toast in oven or toaster oven until golden, 3-5 minutes. Halve tomatoes lengthwise.

Add lettuce and tomatoes to bowl with vinaigrette and toss to combine. Season with salt and pepper

Place burgers on bottom halves of ciabattas, then top with onion and a small amount of salad. Place top halves of ciabattas on top. Divide between plates and serve with remaining salad on the side.