Preheat oven to 375°F (190°C).
Cook 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, about 3-4 minutes.
Add ground beef to the skillet. Cook until browned and cooked through, breaking it up with a spoon, about 6-8 minutes.
Season beef mixture with Italian seasoning, salt, and black pepper. Stir in marinara sauce and simmer for 5 minutes.
In a large mixing bowl, combine cooked tortellini and beef marinara sauce mixture.
Transfer mixture into a shallow white ceramic baking dish.
Sprinkle mozzarella cheese and parmesan cheese evenly over the top.
Bake uncovered for 20-25 minutes until cheese is melted and browned on top.
Let cool for 5 minutes before serving. Scoop portions onto round white plates.