Preheat the oven to 375°F (190°C).
Cook the cheese tortellini according to package instructions until al dente. Drain and set aside.
In a large skillet, heat olive oil over medium heat. Add diced onion and minced garlic; sauté until softened and fragrant, about 3-4 minutes.
Add ground beef to the skillet. Cook, breaking it up with a spoon, until browned and cooked through, about 6-8 minutes.
Stir in Italian seasoning, salt, and black pepper. Pour in the tomato marinara sauce and simmer for 5 minutes.
Combine the cooked tortellini with the beef and sauce mixture, stirring gently to coat evenly.
Transfer the mixture to a shallow white ceramic baking dish. Sprinkle mozzarella and parmesan evenly on top.
Bake uncovered for 20-25 minutes, until the cheese is melted, bubbly, and golden brown with slightly crispy edges.
Remove from oven and let rest for 5 minutes before serving. Scoop portions onto round white plates.