Preheat your oven to 375°F (190°C) and spray a regular-sized muffin pan with non-stick spray.
Unroll the crescent dough and separate it into two large sections along the perforated lines. Cut each section into thirds, then divide each of those sections down the middle, creating 12 squares total. If using round crescent rolls, use one for each muffin cup instead of cutting.
Press each dough square into one of the muffin cups, pressing down into the cup and slightly up the sides.
Spoon about 2 teaspoons of marinara sauce into the bottom of each dough cup, followed by a spoonful of mozzarella cheese.
Place one meatball (can be frozen) into the center of each cup, then top with an additional 2 teaspoons of marinara sauce and more mozzarella cheese.
Bake for 15-17 minutes, until the crescent dough turns golden brown and the cheese is bubbly.
Remove from the oven, allow to cool for a few minutes, then carefully take each cheesy meatball bite out of the muffin pan. Serve with extra marinara sauce if desired.