In a large resealable plastic bag, combine the first 10 ingredients; add lamb chops. Seal bag and turn to coat; refrigerate for 8 hours or overnight.
In a saucepan. saute green onions in butter until tender. Add vinegar and wine or broth and grape juice; bring to a boil. Add mint and sugar. Reduce heat; simmer, uncovered, for 30 minutes or until sauce is reduced to 3/4 cup. Strain; discard mint. Set sauce aside.
Thread onion wedges onto metal or soaked wooden skewers. Brush with salt and pepper. Discard marinade from lamb. Grill chops, covered, over medium-hot heat for 5-6 minutes on each side or until meat reaches desired doneness (for medium, a thermometer should read 160°; well done, 170°). Grill onion skewers for 2-3 minutes or until tender.
In a large skillet, saute green onions and garlic in oil and butter until tender. Add the spinach, salt and pepper; saute for 2-3 minutes or until spinach just begins to wilt and is heated through. Place on a serving platter. Remove onion from skewers; place onion and lamb chops over spinach.