Put the salt in a wide, shallow bowl with the garlic. Mash them together until they form a paste. Add yogurt, lemon, and pepper.
Skin the chicken breasts, remove all visible fat, and separate the halves. Bend each backward to break the bones so the pieces will lie flat. Add chicken to the yogurt mixture and turn so all surfaces are well coated.
Cover the bowl tightly and refrigerate. Allow chicken to marinate at least overnight, up to 1 day and a half. Turn after half the time.
To cook, remove breasts from marinade and wipe off all but a thin film. Broil or grill about 6 inches from the heat source for 6 to 8 minutes per side, or until thoroughly cooked. Meat will brown somewhat but should not char.