Preheat your oven to 375°F (190°C).
In a large pot, boil water and cook the tortellini according to package instructions. Once cooked, drain and set aside.
In a skillet, heat olive oil over medium heat. Add the diced onion and cook until softened, about 3-5 minutes.
Add minced garlic and ground beef to the skillet. Cook until the beef is browned and cooked through, about 8-10 minutes. Drain excess fat.
Stir in crushed tomatoes, tomato sauce, dried basil, dried oregano, salt, and pepper. Let the sauce simmer for about 10 minutes.
In a large bowl, combine the cooked tortellini with the meat sauce, ricotta cheese, and half of the mozzarella cheese. Mix well.
Pour the tortellini mixture into a greased 9x13 inch baking dish. Top with the remaining mozzarella cheese and sprinkle grated Parmesan cheese over the top.
Bake in the preheated oven for 20-25 minutes, or until the cheese is bubbly and golden brown.
Remove from the oven and let it cool for a few minutes before serving. Garnish with fresh basil leaves if desired.