Combine yogurt, oregano, garlic salt, black pepper, cucumber and green onion in a medium bowl. Refrigerate to blend flavors.
Combine oil, lemon juice and rosemary in a resealable plastic bag. Add lamb chops and toss to coat. Marinate a minimum of 15 minutes.
Preheat oven to 350ºF. Remove chops from bag; discard marinade. Place lamb chops on baking sheet; bake 15 to 20 minutes or until 145ºF. Serve with Tzatziki Sauce.