Dice potatoes, onions and peppers into 1/4" pieces.
Heat the oil in a large skillet over medium high heat.
Add the onions and potatoes.
Stir to coat. Season with salt and pepper and stir again.
Spread potatoes across the skillet and let cook for 10 minutes, stirring every few minutes and then spreading the potatoes out again.
You want the potatoes to get brown and crispy on the sides.
Add the peppers and stir to combine. Continue cooking, stirring every few minutes for another 5-10 minutes. Taste and season with salt, pepper and rosemary to taste.