Whisk lime juice, soy sauce, oil and chili powder in a large bowl. Reserve 2 tablespoons of the marinade in a small bowl. Add chicken to the remaining marinade; toss to coat. Marinate in the refrigerator for 20 minutes or up to 1 hour.
Pre-heat grill to medium-high.
Meanwhile, place cilantro, scallions, sesame seeds and the reserved marinade in a food processor and process until fairly smooth.
Oil the grill rack. Remove the chicken from the marinade (discard marinade) and grill until cooked through and no longer pink in the middle, about 2 minutes per side.
Serve the chicken & cilantro-sesame pesto together.
** This grilled chicken works perfectly on a salad as shown in the picture