Preheat your oven to 375°F (190°C).
Boil a large pot of salted water and cook the jumbo shells until they are al dente.
Drain the pasta shells thoroughly and lay them out on a baking sheet to prevent sticking.
Form the ground beef into small, marble-sized mini meatballs.
Sauté the mini meatballs in a large skillet over medium heat until browned and cooked through, then drain any excess fat.
In a mixing bowl, combine the ricotta cheese, egg, chopped parsley, and garlic powder.
Spread a thin layer of marinara sauce on the bottom of a 9×13 inch baking dish.
Stuff each cooked shell with a spoonful of the ricotta mixture and tuck one or two mini meatballs inside each shell.
Arrange the filled shells in the baking dish and cover them with the remaining marinara sauce.
Top evenly with the shredded mozzarella cheese.
Bake for 20-25 minutes, or until the cheese is bubbling and slightly golden.