1. Position rack in lower third of oven, preheat to 450°F.
2. Place potatoes in a large pot, cover with water and bring to a boil. Cook, covered, until fork-tender, about 15 minutes. Drain.
3. Drizzle 1 tablespoon oil on a large rimmed baking sheet. Add the potatoes and, using the bottom of a glass coated with cooking spray, gently smash each potato to flatten. Drizzle with the remaining 1 tablespoon oil and sprinkle with salt and pepper.
4. Bake the potatoes, turning once halfway, until crispy and browned, about 20 minutes. Sprinkle with garlic, Parmesan and lemon zest.