Combine the cilantro, lime juice & zest, olive oil, salt and pepper together in a large zip lock bag and mix well. Add the chicken and seal; place into the refrigerator and marinate for 3 hours.
Remove the chicken from the refrigerator 15 minutes prior to cooking. Heat a grill pan that has been coated with cooking spray over medium heat. Season both sides of the chicken with sea salt and freshly cracked pepper, to taste then place into the hot grill pan. Cook the chicken for 6 minutes on each side or until cooked through and the juices run clear. Let the meat rest for 5 minutes before serving.
While the chicken is cooking combine the avocado, tomato, red onion, cilantro, lime juice, sea salt, and freshly cracked pepper, to taste. Gently mix until well combined. Spoon the salsa over the chicken and serve. Enjoy.