Preheat oven to 350 degrees.
Using a cooking spray or cooking oil, lightly grease a 12 cup muffin tin.
In a small bowl, mix together salsa, ketchup, mustard and brown sugar and set aside.
Cook onions and garlic in olive oil in a small skillet, over medium heat, stirring occasionally, until softened, about 10 minutes.
Remove from heat and let cool.
In a large mixing bowl, combine beef, turkey, carrot, spinach, bread crumbs, parmesan cheese, egg, salt and pepper, using a fork or your hands to mix until combined.
Stir in onion mixture.
Fill each muffin tin to the top with the meatloaf mixture and top with salsa sauce.
Bake meatloaf muffins in the centre of the oven for approximately 20 minutes or until cooked through.
Five minutes before they are finished, sprinkle meatloaf muffins with shredded cheese.