Cover cubed potatoes with cold salted water in a pot.
Bring to a boil, then simmer until barely tender at the edges. Drain well.
Return potatoes to the warm pot and shake to roughen edges. Let steam-dry for a minute.
Heat oil and butter in a large skillet over medium heat until shimmering.
Spread potatoes in an even layer and cook without stirring until golden on the bottom.
Flip and continue cooking, stirring occasionally, until crisp and browned on most sides.
Stir in onion and bell pepper and cook until softened and lightly charred at the edges.
Season with salt, pepper, paprika, and garlic powder. Toss to coat evenly.
Fold in parsley, taste, and adjust seasoning. Serve hot.