Lightly wet a chicken breast with cold water and set it between two sheets of plastic wrap. Pound it into a broad, flat sheet about 1/4-inch thick (called a paillard), using a meat pounder, the side of a heavy cleaver, or a skillet. Pound the other breasts into paillards the same way and arrange them on a baking sheet.
Generously season each paillard on both sides with salt and pepper and a pinch or two of chile flakes. Sprinkle both sides with the garlic and rosemary. Drizzle both sides with the lemon juice and olive oil and pat into the meat with your fingertips. Refrigerate the paillards for 20 minutes while you prepare the grill.
Heat a gas grill to high or prepare a hot charcoal fire. Brush and oil the grill grate.
Arrange the paillards on the grill grate and grill until cooked and firm to the touch, 1 to 2 minutes per side. (Use a long, wide spatula to move and turn the paillards.) Transfer the paillards to a platter or plates. Drizzle with olive oil and serve immediately with lemon wedges for squeezing.
nutrition information (per serving):
Photo: Ben Fink