Place onion and garlic cloves in a food processor; run until finely chopped (but not liquefied). In a large bowl, combine ground turkey with the onion mixture, grated carrots, tomato paste, Dijon mustard, kosher salt, and freshly ground black pepper. Form into 4 patties, each 3/4 inch thick.
Place on a medium-hot grill and cook 5 minutes per side. (Or to cook on the stovetop, heat 2 tablespoons olive oil in a grill pan over medium heat. Place the burgers in the pan and cook 7 to 8 minutes; flip and cook 5 minutes more.) Top with sliced mozzarella (1/4 pound for 4 burgers). Cook 2 to 3 minutes longer, until the cheese melts. Top with crispy bacon and sliced tomatoesand serve on toasted kaiser rolls.