Adjust your toaster oven cooking rack to the bottom position, select the ‘Bake’ setting, and preheat to 400°F. Lightly oil a rimmed baking sheet.
Cut the potatoes in half or quarters if larger. You’re shooting for pieces that are about ½-inch to ¾-inch thick.
In a medium bowl, combine potatoes, olive oil, garlic, rosemary, salt, and black pepper. Toss well to coat.
Transfer potatoes to the prepared baking sheet and arrange in a single layer with the cut sides facing the pan.
Roast potatoes, flipping occasionally, until golden, crispy, and fork-tender about 30 to 45 minutes depending on the size of your potatoes.
