Place the sweet potatoes in a large pot, fill with water, and bring to a boil. Boil for 8 to 15 minutes, or until the potatoes are just fork-tender, but still firm. The exact timing will depend on the size of your potatoes. Let cool and slice horizontally into 1/4-inch rounds.

Preheat a grill to medium-high heat. Toss the sweet potato rounds with oil, pinches of salt and pepper, and chili powder, if desired. Grill 3 to 5 minutes per side, or until char marks form.