1. Prepare a large ziplock bag. Scrub the lemon and insert the lemon and the zester into the bag (this keeps your counters neat and clean!). You should have about one and 1/2 to two teaspoons zest. Add the olive oil, garlic, parsley, salt, and pepper and mix together in the bag.
2. Add chicken cutlets and massage the marinade into the cutlets until they’re evenly coated. Close bag tightly, squeezing out as much air as possible, and place in a bowl in the fridge overnight.
3. The next day, leave the bag out at room temperature for approximately 1/2 hour before grilling.
4. Spray a grill pan with cooking spray and heat over medium-high heat. Grill the cutlets, a few at a time, for three minutes on each side. (If they’re very thin, two and 1/2 minutes is sufficient.) Using a pair of tongs, carefully turn each cutlet over and grill the other side. Continue until all cutlets are done. Spray pan generously with cooking spray in between batches.