Combine the lime juice, cilantro, mustard, olive oil, chili powder, salt, and pepper in a food processor. Pulse until ingredients are well combined.
Place the chickens in a 7-by-11-inch Pyrex baking dish. Pour the marinade over the chicken, cover with foil, and refrigerate for at least 15 minutes or up to 6 hours.
Heat a grill and cook chicken for 5-7 minutes per side until browned and cooked in the center. Serve and enjoy.