You can make this Balsamic Chicken without the citrusor just one of them and it's still delicious!
Clean chicken breasts and put into a 1 gallon ziploc bag.
In a small mixing bowl whisk together the balsamic vinegar, olive oil, and zests or oil (if using). Whisk until emulsified (blended together).
Reserve 3-4 TBS in a separate small bowl for basting. Cover.
Pour the rest of the marinade over the chicken and pop in the fridge for a couple of hours. Try to turn the chicken every 30 minutes or so, if possible.
Preheat grill about 15 minutes before grilling and pull chicken out of fridge.
Discard excess marinade and lay chicken flat on a sheet pan or baking dish.
Salt and pepper both sides of the chicken.
When grill is hot, lay chicken down on the first side cooking 4-5 minutes, depending on the size of the breasts.
Re-whisk remaining marinade if it has separated.
When chicken is ready (not sticking), flip breasts and baste the cooked side with reserved marinade.
Cook second side for another 4-5 minutes or until done. Chicken cooks to 165F, but you can remove it at 160F and let it rest for 5-10 minutes, as it will continue cooking to 165F and reserve its juices as it rests.