Parcook the sweet potatoes: Place in a pot of water and boil until fork-tender; let cool. Cut off the ends and slice into approximately 1/4 - 1/2 inch rounds. Place the rounds on a baking sheet, drizzle with olive oil and sprinkle with salt and pepper; toss to coat.
Place all of the ingredients for the cilantro chimichurri into a food processor and purée until smooth or your preferred consistency. Taste for seasoning. Pour into a small bowl and set aside until ready to serve. Makes 1 cup.
Preheat grill to medium-high heat and oil the grates. Place the sweet potato slices onto the prepared grill and cook for approximately 2 minutes per side or until grill marks appear and they're slightly charred on the edges.
Remove the sweet potato rounds from the grill onto a serving plate and spoon some of the cilantro chimichurri over the top. Serve the remaining chimichurri on the side.