Preheat the oven to 350°F (175°C).
In a skillet over medium heat, brown the ground beef until fully cooked, about 6-8 minutes. Drain excess fat.
Add the diced onion and minced garlic to the skillet, cooking until the onion is translucent, about 3-4 minutes.
Stir in the marinara sauce and Italian seasoning. Let it simmer for about 5 minutes.
Cook the tortellini according to package instructions until al dente. Drain and set aside.
In a large mixing bowl, combine the cooked tortellini with the meat sauce, mixing well to coat evenly.
Transfer the mixture into a greased 9x13 inch baking dish.
Sprinkle the shredded mozzarella and grated Parmesan generously on top.
Bake for 25-30 minutes or until the cheese is bubbly and golden brown.
Remove from the oven and let it sit for 5-10 minutes before serving.
