Prep and preheat: Heat the oven to 375°F (190°C). If you’re not using an oven-safe skillet, lightly coat a 9x13-inch baking dish with nonstick spray.
Brown the beef: Warm a large oven-safe skillet over medium-high heat.
Add a drizzle of olive oil, then the ground beef. Cook, breaking it up with a spoon, until well browned and no longer pink, about 5 to 7 minutes. Drain excess fat if needed.
Add aromatics: Stir in the onion and a pinch of salt.
Cook until softened, 3 to 4 minutes. Add the garlic, Italian seasoning, and red pepper flakes. Cook 30 to 60 seconds, until fragrant.
Build the sauce: Pour in the marinara and beef broth.
Stir, scraping up any browned bits from the pan. Simmer for 3 to 5 minutes to marry the flavors. Taste and season with salt and pepper.
Fold in tortellini: Add the tortellini straight to the sauce.
If using refrigerated tortellini, no need to boil first. Stir to coat evenly.
Cheese layer: Dollop spoonfuls of ricotta over the tortellini. Sprinkle 1 1/2 cups mozzarella and 1/4 cup parmesan evenly on top.
Scatter chopped basil or parsley.
Bake: Transfer the skillet to the oven (or pour into the prepared baking dish). Bake uncovered for 18 to 22 minutes, until the tortellini are tender and the sauce is bubbling around the edges.
Finish under the broiler: Pull the pan out and top with the remaining 1/2 cup mozzarella and 1/4 cup parmesan. Broil on high for 2 to 3 minutes, just until the cheese is melted and lightly golden.
Watch closely.
Rest and serve: Let the bake rest 5 minutes so it sets slightly. Garnish with more fresh herbs. Serve hot with a green salad and garlic bread, if you like.