In a ziploc bag, combine chicken, chopped lemongrass, garlic, soy sauce, sesame oil, sugar and pepper. [Note: To make things easy, I chopped up the lemongrass in a food processor.] Add cayenne pepper if you want this to be spicy. Seal and shake ziploc bag to evenly disperse marinade with the chicken. Place in refrigerator for at least 1 hour, but preferably for 2 hours.
Heat vegetable oil over medium heat. Place chicken on the pan and cook for 7 minutes per side, or until each side is nicely browned and the internal temperature of the thighs is 165˚F (75˚C).
Slice into strips and serve over a bowl of steamed white rice sprinkled with sesame seeds. Garnish with chopped cilantro.