Preheat 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 and sauté until softened and fragrant, about 3-4 minutes.
Add ground beef to the skillet. Season with salt, black pepper, and Italian seasoning. Cook until browned and cooked through, breaking up the meat as it cooks, about 7-8 minutes.
Drain excess fat from the skillet if necessary.
Stir in the tomato marinara sauce and simmer for 2-3 minutes to combine flavors.
In a large mixing bowl, combine cooked tortellini and beef sauce mixture gently.
Transfer the mixture to a shallow white ceramic baking dish.
Sprinkle mozzarella cheese evenly over the top, then sprinkle parmesan cheese.
Bake uncovered in the preheated oven for 20-25 minutes, until cheese is melted and golden brown on top.
Remove from oven and let rest for 5 minutes before serving.
Serve portions scooped onto round white plates.