Preheat the oven to 375 F.
Heat a large skillet over medium-high heat and cook the ground beef, breaking it up with a spoon, until browned and cooked through. Drain any excess grease if needed.
In a baking dish, combine the tortellini, cooked beef, zucchini, and marinara sauce. Stir to combine, then cover tightly with foil.
Bake for 30 minutes, or until the tortellini is tender and the zucchini is cooked through.
Remove the foil, sprinkle the mozzarella cheese evenly over the top, and bake uncovered for 5 minutes, or until the cheese is melted.
Let cool for a few minutes before serving.