In a large bowl toss the potatoes with olive oil, garlic powder, 1/2 teaspoon salt and black pepper to taste, toss to evenly coat.: The moment you begin, inhale the faint aroma of olive oil and garlic powder meeting the raw potatoes . The oil should glisten on each quartered piece, and you want all surfaces lightly coated so heat transfers uniformly when steaming. As you toss, notice the tactile shift from dry to slightly slick, which signals even seasoning distribution. This matters because uneven coating leads to pockets that are under seasoned or dry after cooking. A common mistake is over tossing and mashing the potatoes ; be gentle and use a large bowl so the pieces have room to move.
Transfer to a large sheet, 18 x 18 inches of heavy duty foil on a flat surface.: When you spread the seasoned potatoes onto the foil, they should form a loose pile in the center, not a single compressed mound. The foil will cradle steam, so leave some breathing room around the edges to fold and seal. You will hear a faint metallic hiss when you shape the packet later, but at this stage focus on spacing. Avoid placing them too close to the foil edge, which can make sealing awkward and cause leaks later.
Place the ingredients in the center of the foil. Form a packet by bringing the short ends of the foil together and fold twice to seal leaving room for steam.: As you fold, feel the give of the foil and the slight weight of the potatoes inside. The goal is a tight seal with some internal space so steam can circulate and tenderize the pieces. Folding twice ensures a more secure packet, and leaving room for steam prevents bursting. A frequent error is sealing the foil too tightly with no airspace, which steams unevenly and can make the texture gummy.
Grill, covered over medium heat 30 minutes, shaking the bag every 10 minutes so the bottom of the potatoes don’t burn. Open carefully and top with 1/8 teaspoon salt, lemon zest and parsley.: As the packets warm on the grill, you will hear subtle sounds of moisture moving, a soft sizzle at the edges where the foil meets heat, and you may smell a faint roasted note as the skins begin to concentrate flavor. Shaking every 10 minutes redistributes heat and prevents one side from sitting on a hot spot and charring. When you open the packet, steam will puff up like a warm breath, releasing bright citrus and herb perfume. Sprinkle the finishing salt , lemon zest , and parsley while the potatoes are hot so they absorb the aromatics. Be careful of the steam and open away from your face, as a common mistake is steam burns from impatient opening.
Bake in a preheat 400 F oven 35 to 40 minutes, shaking the halfway. Open carefully and top with 1/8 teaspoon salt, lemon zest and parsley.: In the oven approach, you will notice the foil warming quickly and the kitchen filling with a cozy roasted scent. Shaking halfway redistributes the pieces so edges get exposure and nothing sticks to one side. Check for visual cues, like slightly translucent edges and tender centers when pierced with a fork. If you skip the halfway shake, some pieces may overcook on one side, becoming dry or tough. Opening the packet will release a bright citrus steam, and the final sprinkle of salt , lemon zest , and parsley will revive the flavors and add a vibrant finish.