Preheat the oven to 375°F.
Spray a lined baking sheet with the cooking spray.
In a large bowl, combine the beef, pork, onion, breadcrumbs, ½ cup tomato sauce, eggs, Worcestershire sauce, 2 tbsp balsamic vinegar, thyme, parsley, cheese, salt, and pepper.
Mix all the ingredients with clean hands until fully mixed.
Rinse a loaf pan (8" x 4") with water and then pack the meat mixture into the wet pan.
Invert the pan over the greased baking sheet and gently transfer onto the sheet.
Bake for 50 minutes.
Meanwhile, mix 3 tbsp tomato sauce with 1 tbsp balsamic vinegar. Set aside.
After 50 minutes, remove the meatloaf from the oven and brush the tomato/balsamic sauce over the top of the loaf and return to the oven to bake for another 20 minutes. Save some of the sauce for another brushing after the meatloaf has finished cooking.