Combine the olive oil, lime juice, cilantro, garlic, sugar, salt, and pepper in a large Ziploc bag. Place chicken in a bag with marinade and refrigerate for 30 minutes to 8 hours.
When ready to grill preheat to medium to medium-high heat (about 400 degrees F). Lightly oil the grate. Place chicken on the grill and grill for 5-7 minutes per side or until a meat thermometer reads 165°F.
Remove from grill and allow to rest for 10 minutes.
If your chicken breasts are very large cut them in half horizontally for quicker cooking.