Brown the Beef: Heat olive oil in a large, 12-inch oven-safe skillet over medium-high heat. Add the ground beef and chopped onion. Cook, breaking up the meat with a spoon, until the beef is no longer pink and the onion is soft (about 5-7 minutes). Drain any excess grease.
Bloom Spices: Add the minced garlic and cook for 30-60 seconds until fragrant. Stir in the chili powder, cumin, paprika, oregano, salt, and pepper. Cook for another minute to toast the spices.
Create the Sauce: Pour in the red enchilada sauce and the undrained can of diced tomatoes with green chiles. Stir well, scraping up any browned bits from the bottom of the pan. Bring to a simmer.
Cook Tortellini: Add the frozen tortellini directly to the simmering sauce, stirring gently to coat. Cover the skillet, reduce heat to medium-low, and cook for 5-7 minutes, or until the tortellini is tender (al dente).
Melt the Cheese: Turn off the heat. Sprinkle the shredded cheese blend evenly over the top. For a bubbly, golden-brown top, place the skillet under the oven broiler for 1-3 minutes (watch carefully!). Alternatively, cover with a lid for 2-3 minutes to melt the cheese.
Rest and Serve: Let the casserole rest for a few minutes before serving. Garnish with your favorite toppings and enjoy!