Peel the potatoes (2) and cut them into small cubes. Place cubed potatoes in a bowl of cold water, swishing them around to remove starch. Drain in a colander and rinse. Spread potatoes out on paper towels and pat dry.
Add oil (3 tablespoons) to a cast iron skillet and heat over medium-high heat. Add the potatoes and cook, stirring as needed, until the potatoes are fork-tender and browned on most sides.
Sprinkle potatoes with 1/2 teaspoon salt and 1/4 teaspoon black pepper. Transfer to a plate and set aside.
Stir in the onions (1 cup), red bell pepper (1), and garlic (2-3 cloves) into the skillet. Cook over medium heat, stirring until golden brown.
Stir in the beef (8 ounces), chili powder (1/2 teaspoon), and 1/2 teaspoon salt, and 1/4 teaspoon black pepper, and cook, breaking up any clump, until brown, about 5 minutes. Drain any excess fat.
Add the potatoes back to the skillet and mix in. Sprinkle cheese (1 1/2 cups) evenly over the top of the skillet.
Place skillet under the preheated broiler until cheese is melted, about 1 minute. Garnish with fresh parsley and serve.