1 teaspoon freshly ground black pepper, plus more as needed
1/4 cup olive oil
1 medium yellow onion, large dice
1 medium red potato, quartered and thinly sliced crosswise
2 medium red bell peppers, thinly sliced
4 medium garlic cloves, finely chopped
1/4 cup finely chopped Italian parsley
Heat the broiler on high and arrange a rack in the middle.
Whisk the eggs, 1 cup of the cheese, and the measured salt and pepper in a large bowl until the eggs are smooth; set aside.
Heat the oil in a large, ovenproof frying pan over medium heat. When it shimmers, add the onion and season with salt and pepper. Cook, stirring occasionally, until tender, about 4 minutes. Add the potato and cook, stirring occasionally, until the edges become tender, about 4 minutes. Add the bell peppers and garlic and cook, stirring occasionally, until just tender, about 8 minutes. Add the parsley and stir to incorporate.
Pour the reserved egg mixture over the vegetables and reduce the heat to medium low. Cook until the eggs are set around the outer inch of the pan, about 10 to 15 minutes. Sprinkle the remaining cheese evenly over the frittata and place it under the broiler until puffed, golden, and completely set in the center, about 4 to 6 minutes. Let sit 5 minutes before serving.