Trim any visible fat from the chicken breasts and pound or trim them so they are an even thickness.
Make several small crosswise slits in each breast to allow the marinade to penetrate and to help the thicker parts cook evenly.
Place the chicken in a zip-top bag or an airtight container and pour in your marinade, making sure all pieces are coated.
Refrigerate and marinate for 4–6 hours, turning occasionally; you may marinate longer if desired.
When ready to cook, preheat the grill to medium-high and oil the grates or spray with nonstick spray.
Place chicken on the grill diagonally and cook about 4 minutes, then rotate the pieces to create crosshatch grill marks and cook another 4 minutes.
Flip the chicken and cook about 4 minutes more, or until the chicken feels firm and an instant-read thermometer registers 165°F (75°C).
Remove from the grill, let rest briefly, and serve hot garnished with chopped cilantro if desired.