Pour the olive oil into a large nonstick skillet and warm over medium-high heat until shimmering.
Add the diced potatoes, stir with a spatula to coat with the oil, shake the pan to distribute the potatoes into one even layer, and then let them cook, without stirring, for a few minutes or until the potatoes develop a nice golden crust on that side.
Stir the potatoes with a spatula and repeat this process, letting the potatoes cook and become golden on all sides, stirring occasionally, for about 20 minutes. If the potatoes start to burn, reduce the heat. If they are not browning, turn up the heat a bit.
Once the potatoes are nice and golden and crispy (and tender on the inside), stir in the minced rosemary, garlic powder, salt, and pepper.