Preheat the oven to 400°F (200°C) and grease a 12-cup muffin tin.
Prepare the vegetables: In a food processor, combine onion, carrot, celery, parsley, and garlic. Pulse until finely chopped.
Mix the meatloaf ingredients: In a large bowl, combine the ground beef, breadcrumbs, egg, Worcestershire sauce, salt, pepper, and the minced vegetables. Mix until just combined.
Shape the muffins: Divide the meat mixture evenly into the muffin tin, loosely packing each cup.
Make the glaze: In a small bowl, whisk together barbecue sauce (or ketchup), brown sugar, Dijon mustard, and cumin.
Bake the meatloaf muffins for 20 minutes. Remove from the oven, brush with the glaze, and return to bake for an additional 10-15 minutes until fully cooked and browned.
Serve: Let the muffins cool for a few minutes before serving.