Trim fat from chops; discard fat. Season chops with garlic salt and pepper. Grill chops on an uncovered grill directly over medium coals for 8 to 10 minutes or until medium doneness, turning once. (Or, in a large skillet cook chops in 1 tablespoon hot cooking oil over medium heat about 10 minutes or until medium doneness, turning once.) Transfer chops to a paper-towel-lined dish to drain; set aside.
For relish, in a medium skillet heat oil. Cook apple, shallots, brown sugar, and cloves in the hot oil, uncovered, over medium heat for 3 minutes or until just tender. Add blackberries; reduce heat. Cook mixture, uncovered, for 5 minutes, stirring often. Cool. Cover and chill, if desired.
To serve, using a sharp knife carefully remove meat from bones. Spoon one-fourth of the blackberry relish onto cut side of each roll bottom. Top with watercress sprigs. Arrange two of the boned, cooked chops on top. Cover with roll tops. Makes 4 servings.