Place peppercorns and coriander seeds in a large skillet over medium-high heat; cook 1 minute or until toasted. Place peppercorns and coriander seeds in a spice or coffee grinder; process until finely ground.
Combine the pepper mixture, cilantro (if desired), and next 4 ingredients (cilantro through garlic). Loosen skin from chicken breasts and thighs by inserting fingers, gently pushing between skin and meat. Rub the seasoning mixture under loosened chicken skin. Seal and marinate in the refrigerator 3 to 8 hours. Remove chicken from bag. Place chicken on grill rack coated with cooking spray; grill 8 minutes on each side or until chicken is done. Discard skin.