garnishes: grilled lime wedges, cotija or feta crumbles, chopped cilantro
Put a large pot of salted water on the stove and bring to a boil. Cut each sweet potato lengthwise into 4 pieces (or 6 pieces if large.) Transfer to pot and simmer for about 15 minutes until just barely fork tender, but not mushy. You want them to retain their shape on the grill.
Drain, being careful not to crush the potatoes, and dry well.
Preheat grill (or indoor grill pan) to high heat. You want it to get super hot for a nice char on the potatoes. Place sweet potatoes on foil-lined baking sheet or platter, then drizzle with olive oil and sprinkle with chili powder, salt and pepper.
Grill on each side until lightly charred and crispy. Remove to serving dish and add grilled lime wedges, crumbled cotija or feta cheese, chopped cilantro, and another pinch of sea salt, to taste. Eat!