Marinade: In a small bowl, whisk together the olive oil, garlic, red pepper flakes, oregano, rosemary, and lemon zest.

Thread alternating pieces of chicken and grapes onto 12-inch skewers. Place the skewers into a nonreactive dish or pan. Pour the prepared marinade over the skewers, turning to coat each one. Marinate in refrigerator for 4 to 24 hours.

Remove skewers from marinade, and let excess oil drip off. Discard any remaining marinade. Season the skewers with salt. Grill on a hot barbecue until the chicken is cooked through, 3 to 5 minutes on each side. Arrange on a serving platter and drizzle with the lemon juice.