Step 1: Make the marinade / sauce: Place the garlic, 2 tablespoons of sugar, and the pepper in a mixing bowl. Pound to a paste with the back of a wooden spoon. Stir in the remaining sugar, lime juice, and fish sauce and whisk until the sugar crystals are dissolved. Whisk in the cilantro, chiles, and 1/4 cup water. Set the marinade aside.

Step 2: Cut the chicken sharply on the diagonal into 1/4-inch thick slices (each breast should yield about 4 slices). Make three 1 inch slits in each slice, one an inch from the top and one an inch from the bottom, and one in the middle.

Step 3: Trim the dark green leaves off the lemongrass stalks. Cut each stalk crosswise into 3 inch pieces. Insert 1 piece of lemongrass in each chicken slice, in the slit in the top, through the middle, and out the slit in the bottom. Arrange the skewers in a baking dish in a single layer.

Step 4: Spoon half the marinade over the chicken turning the pieces to coat both sides. Marinate in the refrigerator for 2 hours. Reserve the remainder of the marinade for serving.

Step 5: Drain the chicken well on a wire rack over a rimmed baking sheet. Lightly brush on both sides with sesame oil.

Step 6: Set up your grill for direct grilling and preheat to high. Brush or scrape the grill grate clean and oil it well. Arrange the skewers on the grate. Grill until sizzling and browned on both sides and the chicken is cooked through, 1 to 2 minutes per side. Serve at once with the remaining marinade / sauce in small bowls for spooning on top. Sprinkle with the scallions, chopped peanuts, or sesame seeds, and you’re in business.