Preheat the oven to 350°F or 175°C and lightly grease a baking dish.
Sauté the diced onion in olive oil over medium heat until soft, then add the ground beef and cook until browned, draining excess fat if needed.
Stir in the enchilada sauce, garlic powder, cumin, salt, and pepper, and simmer for about 5 minutes.
Cook the tortellini according to package directions and drain well.
Gently mix the cooked tortellini with the beef mixture until evenly coated.
Transfer everything to the baking dish and sprinkle shredded cheese evenly over the top.
Bake uncovered for 20 to 25 minutes until the cheese is melted and bubbly.
Let rest briefly before serving to help the casserole set.