Reserve 1 1/2 cups dip as serving sauce. In a large resealable plastic bag, combine remaining 1 cup dip, lamb, zucchini, and onion. Close and shake to thoroughly coat meat and vegetables. Let marinate 30 minutes at room temperature. (Can be stored in refrigerator up to 24 hrs in advance.)
When ready to cook, heat a lightly-oiled grill pan over medium heat. Remove lamb and vegetables from marinade, let excess drip off, and thread on skewers. Place skewers in pan and cook, turning to cook all sides, until lamb is medium-rare and vegetables are cooked through, about 6 minutes total. (You may have to do this in batches.)
Serve immediately over rice or with flatbread and pass reserved sauce on side.
Serving Suggestion: Steamed rice, rice pilaf, or pita bread.
In a medium bowl, mix together yogurt, cucumber, dill, coriander, red pepper flakes, vinegar, and salt until evenly combined. Season well with freshly ground black pepper, taste, and adjust seasoning, as needed. Serve with an assortment of vegetables for dipping.
Serving Suggestion: Assortment of vegetables such as green beans, celery, cucumber, mushrooms, roasted beets, or boiled potatoes.