For Marinade: Process all ingredients in food processor until smooth, about 15 seconds. Reserve 2 tablespoons marinade; transfer remaining marinade to medium bowl.
For Shrimp: Pat shrimp dry with paper towels. To butterfly shrimp, use paring knife to make shallow cut down outside curve of shrimp. Add shrimp to bowl with marinade and toss to coat. Cover and refrigerate for at least 30 minutes up to 1 hour.
Prepare your grill, clean and oil so the shrimp want stick. Thread marinated shrimp on skewers. (Alternate direction of each shrimp as you pack them tightly on skewer to allow about a dozen shrimp to fit snugly on each skewer.)
Sprinkle 1 side of skewered shrimp with sugar. Grill shrimp, sugared side down, over hot side of grill, until lightly charred, 3 to 4 minutes. Flip skewers and move to cool side of grill and cook, covered until other side of shrimp is no longer translucent, 1 to 2 minutes. Remove and toss with reserved marinade. Sprinkle with cilantro and serve.