In a small bowl, mix together the cumin, oregano, and red pepper flakes (if using).
In a large skillet, warm 1 tablespoon oil over medium heat. Once the oil is hot, add the beef, and break it into chunks. Sprinkle ½ teaspoon salt all over and cook, continuing to break into smaller chunks, until cooked through, about 5 minutes. Stir in about half of the spices. Transfer to a bowl.
Wipe the skillet out, then add the remaining 1 tablespoon oil over medium-high heat. Add in the veggies and remaining ½ teaspoon salt. Cook until veggies are tender and any liquid has evaporated, about 5 minutes. Stir in the remaining spices, garlic, and the cooked beef.
Add the enchilada sauce and stir to combine. Simmer over low heat for 2 minutes, then stir in the tortillas so they get coated in the sauce (try to spread them out evenly), then top with cheese. Remove from heat and transfer to the broiler for 1-2 minutes or until melted and light golden in spots (keep an eye on it!) OR cover with a lid (or a baking sheet) until the cheese melts.
Serve topped with desired toppings!