Wash the potatoes. Use a fork to prick holes on all sides of the potatoes.
Wrap the potatoes individually in damp paper towels. Microwave each potato on high, one at a time, until fork-tender, about 6-7 minutes per russet potato or 5 minutes per sweet potato. Remove the paper towels and allow the potatoes to rest until cool enough to handle.
Slice each potato in half lengthwise. Brush or rub all sides of the potatoes with olive oil. Sprinkle with salt, pepper, and garlic powder, to taste.
Preheat a grill (or indoor grill pan) over medium-high heat. Grill the potatoes flesh-side down until you can see grill marks, about 5 minutes. Flip the potatoes over and place them on the upper rack of the grill (or on indirect heat) to keep them warm and to allow the skin to get crispy, about 5 more minutes.
Garnish the potatoes with optional toppings just before serving.