In a large plastic bag or bowl with a lid, combine lime juice, sugar, olive oil, cilantro, rosemary, garlic, salt and pepper. Remove 1/2 cup marinade; set aside for basting. Add lamb and onions; close plastic bag or place lid on securely. Refrigerate for 30 minutes, turning the bag or stirring every 10 minutes.
Preheat grill. Remove lamb and onions from marinade. Thread lamb, onions and peaches onto 8 skewers. Grill for 10 to 15 minutes, or until done, basting with reserved marinade. Serve hot.
Servings: 4