Fill a medium heavy-bottomed pot with cooking oil and place it over medium heat. Trim off both ends of the green plantain, then make three lengthwise cuts through the skin, each about two inches apart. Peel the skin off the plantains.
Slice the plantains into 1 1/2-inch thick rounds.
When the oil is at 350°F, add the sliced plantains, working in batches to not crowd the pot. When the plantain slices change in color from bone white to a golden yellow (about 3 to 4 minutes) remove them from the pot and drain them on a paper towel-lined plate.
Add about 4 inches of water to a bowl large enough to hold the plantains. Add the garlic powder and the vinegar to the water and mix. Soak the fried plantains for 1 minute and dry them on the paper towel-lined plate.
Add two sheets of parchment to your work surface and ready a heavy skillet. Place one slice of fried plantain on one sheet of parchment, then top it with the second piece of parchment. Use the heavy skillet to smash the plantain flat, about 1/4 inch thick. Set aside and repeat with the remaining slices.
Turn the heat up on the oil. When the oil has reached 375°F, fry the plantains again, working in batches so the pot isn't crowded. Fry the tostones until golden and crispy, about 3 minutes. Drain on the paper towel-lined plate and sprinkle with 1/8 teaspoon salt immediately. Serve with your favorite dipping sauce and enjoy!