Preheat the oven to 400 degrees. Combine the Italian sausage, grated zucchini, breadcrumbs, egg, and garlic powder in a mixing bowl until evenly mixed.
Divide the mixture into eight portions and press each into the cups of a muffin tin.
Bake for 15 minutes until the meatloafs reach an internal temperature of 160 degrees.
While the meatloafs bake, warm the marinara sauce in a skillet over medium heat.
Remove the meatloafs from the tin and place them in the skillet with the sauce. Simmer for 3 to 5 minutes.
Sprinkle the mozzarella over the meatloafs and cover the skillet for 1 minute until the cheese melts.