Preheat the oven to 375°F (190°C).
In a large skillet, cook the ground beef, onion, and garlic over medium heat until the beef is browned.
Add crushed tomatoes, beef broth, Italian seasoning, salt, and pepper. Simmer for 10 minutes to deepen flavor.
Stir in the cheese tortellini and half of the mozzarella cheese.
Transfer the mixture to a baking dish and spread evenly.
Top with the remaining mozzarella cheese.
Bake for 25–30 minutes, or until the cheese is bubbly and golden.
Remove from the oven and let the casserole rest for a few minutes before serving.