shrimp: peeled and deveined, tails removed chiles: stemmed and finely chopped lemongrass: trimmed, bruised with a mallet, and cut into 5cm pieces skewers: soaked in water for 30 minutes lettuce: crisp inner leaves only
Combine shrimp, oil, chiles, lemongrass, ginger, salt, and pepper in a bowl; toss to combine. Cover and refrigerate at least 4 hours or up to overnight.
Heat a charcoal grill or set a gas grill to high; bank coals or turn off burner on one side. Heat a plancha or flat cast-iron griddle over coals until very hot. Remove shrimp from marinade and thread onto skewers; grill on plancha, flipping once, until slightly charred and cooked through, about 3 minutes. Remove shrimp from skewers and serve with radishes, carrots, cilantro, and Thai basil leaves in lettuce leaves; drizzle with sweet chile sauce.