Preheat oven to 375°F (190°C) and spray a 9x13-inch baking dish with nonstick spray.

Heat olive oil in a large skillet over medium heat. Add chopped onions and cook for 3-4 minutes until translucent. Add minced garlic and cook for 30 seconds until fragrant, then add ground beef. Break it up with a wooden spoon and cook for 6-8 minutes until no pink remains and meat develops a golden-brown color.

Stir in marinara sauce and Italian seasoning, then reduce heat to low. Let the mixture simmer for 5 minutes, allowing the flavors to meld together.

While the sauce simmers, cook tortellini in a separate pot (at least 4-quart) according to package directions until al dente. Drain well and set aside.

Combine the cooked tortellini with your meat sauce, stirring gently until every piece is coated. Transfer this mixture to your prepared baking dish and spread it evenly.

Top generously with shredded mozzarella and sprinkle grated Parmesan cheese over the top. Bake for 25-30 minutes until the cheese is melted, bubbly, and golden brown on top. Let it rest for 5 minutes before serving.