Heat the oven to 350 F and spray a 1 1/2 to 2-quart baking dish with cooking oil spray.
Heat the oil in a large skillet over medium-high heat. Add the ground beef and onion and cook for 4 to 6 minutes, until the beef is no longer pink. Add the garlic and seasonings and cook for 1 minute longer. Stir in the refried beans.
Arrange half of the tortilla strips in the prepared baking dish and top with all of the burrito beef mixture, diced tomatoes, and cilantro, if using. Top with the remaining tortilla strips and then sprinkle with the cheese. Cover the baking dish with foil. At this point you may refrigerate the casserole overnight.
Bake the burrito casserole for 15 minutes. Remove the foil and continue to bake for about 5 to 10 minutes, or until the filling is hot and the cheese has melted.
Note: if it was refrigerated, bake covered for about 25 minutes, then remove the foil and bake until hot and the cheese has melted.