Prep. Preheat the oven to 400°F. Lightly spray a 12-cup muffin/cupcake tin with cooking spray and set aside.
Make the tomato sauce. In a small bowl, combine tomato sauce, light brown sugar, and mustard. Mix until combined and set aside.
Mix the meatloaf mixture. In a large mixing bowl, combine all remaining ingredients and add 1/4 cup of the tomato sauce mixture to the meat mixture; using a wooden spoon, mix until everything is well incorporated.
Fill the muffin pan. Divide the meat mixture evenly and place it into the previously prepared muffin pan. Place the muffin pan on a baking sheet.
Bake. Bake for 25 to 28 minutes or until the internal meatloaf's temperature reaches 165°F.
Add the sauce. Remove from oven and top each mini meatloaf with two tablespoons of the prepared tomato sauce mixture; bake for an additional 5 minutes or until the sauce is set.
Cool and serve. Remove from oven and let stand for at least 5 minutes. Plate and serve with remaining tomato sauce.