In a large oven-safe skillet, over medium heat, add the ground beef. Cook until browned, about 5-7 minutes. Drain excess fat if necessary.
Add the chopped onion, minced garlic, and diced bell pepper to the skillet. Sauté for about 3-4 minutes until the vegetables are softened.
Pour in the marinara sauce and beef broth into the skillet. Stir in the tortellini, Italian seasoning, salt, and pepper. Bring the mixture to a gentle simmer.
Once the tortellini is slightly softened (about 5 minutes), sprinkle the shredded mozzarella and grated Parmesan cheese evenly over the top.
Transfer the skillet to the preheated oven and bake for 20-25 minutes, or until the cheese is bubbly and golden brown.
Remove from the oven and let it cool slightly. Garnish with fresh basil if desired before serving.