Cut the potatoes into quarter-inch-thick slices and set them aside. Then, place a skillet on medium-high heat and cook the oil.
Add the potatoes to the pan and season with pepper, rosemary, and salt, then cook for four to five minutes untouched. The undersides should develop a golden crust.
Flip the potatoes and cook the other sides for another four to five minutes, then season with chili powder and garlic powder. Stir the potatoes as they cook for two more minutes, so the seasoning incorporates.
Transfer the fried potato slices to a plate and serve warm.