Place the cubed potatoes in a pot of well-salted cold water. Bring to a boil over high heat, then reduce to a steady simmer. Cook for 6-7 minutes, until a fork slides in with slight resistance. Drain and let steam-dry in the colander for 5 minutes.

In a large bowl, toss the dried potato cubes with the paprika, garlic powder, onion powder, salt, pepper, and cayenne if using. Coat evenly.

Place a 12-inch cast iron skillet over medium-high heat for 2-3 minutes. Add 2 tablespoons of oil and let it heat until it shimmers and moves easily in the pan.

Add the potatoes in a single layer. Do not stir. Cook undisturbed for 3-4 minutes until the bottom side is deep golden brown. Flip carefully with a spatula and cook another 3-4 minutes on the second side.

Push the potatoes to the edges of the pan. Add the remaining 1 tablespoon of oil and add the diced onion and bell pepper. Cook, stirring occasionally, for 4-5 minutes until the onion is softened and beginning to color. Toss everything together.

Spread everything back into an even layer and cook for another 2-3 minutes without stirring to restore some of the crust. Taste and adjust seasoning.

Remove from heat. Toss with fresh parsley and serve immediately.