Preheat the oven to 190°C (375°F). Lightly grease a 9x13-inch baking dish.

Cook the beef mixture: Heat olive oil in a large skillet over medium-high heat. Add onion and cook 3–4 minutes until softened. Stir in garlic for 30 seconds.

Brown the beef: Add ground beef, Italian seasoning, salt, pepper, and red pepper flakes (if using). Cook until browned, breaking it up as it cooks. Drain excess fat if needed.

Add sauce: Stir in marinara sauce and water (or broth). Simmer 2–3 minutes.

Add spinach (optional): Stir in baby spinach and cook just until wilted.

Add tortellini: If your tortellini package says it needs boiling first, boil it according to package directions and drain. If it’s “refrigerated and ready in minutes,” you can usually add it straight to the sauce (check your package). Stir tortellini into the skillet until well coated.

Assemble: Pour the tortellini and sauce mixture into the baking dish. Dot ricotta over the top in small spoonfuls.

Cheese it up: Sprinkle 1 1/2 cups mozzarella over everything, then finish with parmesan.

Bake: Bake uncovered for 20 minutes, until bubbly and lightly golden.

Finish: Sprinkle remaining 1/2 cup mozzarella on top and bake 5 more minutes until melted. Rest 5 minutes before serving. Add basil or parsley if you like.