Sprinkle pepper on one side of each chicken cutlet. Heat oil in a large skillet; brown garlic in oil, then add chicken, pepper-side-down. Saute chicken until cooked through and juices run clear, about 12 to 15 minutes.
In a small bowl combine the mayonnaise, mustard and rosemary. Mix together and spread mixture on 4 slices focaccia bread. Place 1 chicken cutlet on each of these slices, then top each with another bread slice.