1. For sauce, in a small bowl stir together yogurt and dill. Cover and refrigerate until ready to serve.
2. In a small saucepan bring water to boiling. Stir in bulgur and 1/4 teaspoon of the salt. Reduce heat to low. Cook, covered, for 10 minutes. Remove from heat. Let stand, covered, for 5 minutes.
3. Meanwhile, in a large bowl combine the onion, parsley, garlic, coriander, thyme, black pepper, and the remaining 1/4 teaspoon salt. Stir in cooked bulgur and ground lamb; mix well. Shape meat mixture into six 1/2-inch-thick patties. Place in a shallow baking pan. Bake in a 350 degrees oven for 20 to 25 minutes or until meat is done (160 degrees ).
4. To serve, arrange the cucumber ribbons on bottoms of rolls. Add burgers, sauce, tomato slices (if desired), and roll tops.