Lemongrass paste may be substituted and can be found in your grocer's produce department. Once you're turned onto lemongrass, you will look every which way to incorporate this wonderful ingredient into your meal planning.
In bowl of food processor, place canola oil, rice vinegar, sugar, salt, lemongrass, ginger and garlic cloves. Process until lemon grass is chopped fully, about 3 minute Transfer to glass bowl. Add chicken thighs to bowl. Cover and refrigerate at least two hours, or overnight, or up to 2 days.
Prepare charcoal or gas grill. On skewers, thread chicken pieces and scallions, alternating. Place on grill and cook, turning once, until chicken is firm and opaque, about 6 - 8 minute per side. Plate on serving platter and sprinkle with toasted sesame seeds.