Preheat the oven to 425°F.

Line a large baking sheet with parchment paper.

Dice the potatoes into 1/2-3/4-inch pieces. Finely dice the red onion and bell peppers.

Arrange the potatoes and vegetables on the baking sheet. Drizzle with the olive oil, and sprinkle with the garlic powder, paprika, cayenne, salt, and black pepper. Stir with a rubber spatula to coat the potatoes evenly in oil.

Roast the potatoes on middle rack of oven, stirring and flipping with a rubber spatula halfway through the cooking time, until the potatoes are tender, browned, and crispy, 25-30 minutes.

Check to see that potatoes are done. Remove from oven or add time as needed.

Serve the potatoes immediately, with ketchup, if desired.