Place the potatoes in a large pot. Add the salt and enough water to cover the potatoes by 2 inches. Bring the water to a boil over high heat, then reduce to a low boil until the potatoes are barely fork tender, about 15 minutes. If your potatoes are larger, they may take a bit longer.
Drain the potatoes. Dump them on a large baking sheet and place them in the oven for 2-3 minutes to dry off. Remove them from the oven and, once cool enough to handle, coat them in the oil then sprinkle the garlic powder, onion powder and black pepper on them. Spread them out evenly on the baking sheet. Using the bottom of a dry measuring cup or a potato masher, gently press down on each potato to squish them until they're about 1/2 inch thick.
Use a pastry brush to brush the oil from the tray onto the newly exposed insides of the potatoes.
Bake until the potatoes are golden and crispy, about 35-45 minutes. Do not flip. Serve immediately.