Making the marinade takes minutes, but the elapsed time is to allow the flavors to marinate. Chicken thighs also work well, especially on the outdoor grill. We like to serve with sliced avocado. Don't leave the chicken marinating longer than 2-3 hours as the acid from the lemon juice could start to break down the chicken breast.
One at a time, place chicken breasts between sheets of plastic and pound to get an even thickness. Juice lemons, remove seeds but any pulp bits are fine. In a small glass bowl, whisk lemon juice into extra virgin olive oil. Smash and dice garlic cloves, dice shallots and then add both to bowl. Add remaining ingredients, whisk to incorporate. Pour over pounded chicken breasts into ziploc bag and leave in refrigerator for 2-3 hours. When ready to cook, remove chicken from bag and scrape off as much of the garlic and shallot as possible as the little bits will burn. Cook chicken on both sides until done.