PREPARATION:

1. Prepare grill for direct cooking. Meanwhile, heat small skillet over medium heat until hot. Add pine nuts; cook 30 to 45 seconds until light brown, shaking pan occasionally.
2. Combine lamb, pine nuts, yellow onion, 2 cloves garlic, salt and pepper in large bowl; mix well. Shape mixture into 4 patties, about 1/2 inch thick and 4 inches in diameter. Combine yogurt, sugar and remaining 1 clove garlic in small bowl; set aside.
3. Brush 1 side of each patty and red onion slice with oil; place on grid, oiled sides down. Brush tops with oil. Grill, on covered grill, over medium-hot coals 8 to 10 minutes for medium or to desired doneness, turning halfway through grilling time. Place bread on grid to toast during last few minutes of grilling time; grill 1 to 2 minutes per side.
4. Top 4 bread slices with patties and red onion slices; top each with 3 cucumber slices and 1 tomato slice. Dollop evenly with yogurt mixture. Top sandwiches with remaining 4 bread slices. Serve immediately.