Heat 1 tablespoon of vegetable oil in a large skillet (preferably cast iron or non-stick) over medium-high heat. Add the diced potatoes in a single layer. Cook without stirring for 4-5 minutes to get a golden crust, then stir and continue cooking for another 10-12 minutes, stirring occasionally, until potatoes are tender and crispy on all sides. Transfer to a plate and set aside.
In the same skillet, add the remaining 1 tablespoon of oil. Add the diced onion and bell peppers. Cook for 4-5 minutes until they begin to soften. Push vegetables to the side of the skillet. Add the ground beef to the center, breaking it up with a spatula. Cook until no longer pink, about 5-7 minutes, then mix with the vegetables.
Sprinkle the Southwest seasoning blend, salt, black pepper, and red pepper flakes (if using) over the beef and vegetable mixture. Stir well to coat everything evenly. Return the cooked potatoes to the skillet and stir gently to combine all ingredients. Reduce heat to medium-low.
Sprinkle the shredded cheese evenly over the top of the skillet mixture. Cover the skillet with a lid (or a large baking sheet if you don't have one) and let it cook for 2-3 minutes, just until the cheese is fully melted. Remove from heat and sprinkle with fresh chopped cilantro.
Serve the dish directly from the skillet at the table. Garnish individual portions with a dollop of sour cream, a spoonful of salsa, and a lime wedge on the side for squeezing over.