Heat the oven to 375°F. Lightly grease a 12-cup muffin pan.
In a large bowl, combine the ground turkey, oats, grated carrot, egg, onion, milk, Worcestershire sauce, garlic powder, salt, pepper, and 2 tablespoons of the ketchup. Mix gently until just combined.
Divide the mixture among 8 muffin cups, filling each about three-quarters full. Press lightly to shape the tops, but avoid packing the mixture tightly.
In a small bowl, stir together the remaining ketchup, apple cider vinegar, and brown sugar. Spoon the mixture over the meatloaf muffins.
Bake until the muffins are cooked through and the centers reach 165°F, about 25 to 30 minutes. Let them rest in the pan for 5 minutes before removing.