Mix all the spices, the lemon and the tomato paste into the Greek yogurt and then coat the chicken with marinade. Let sit in the refrigerator for at least 3 hours or as long as overnight.
Cut the veggies into large cubes about the same size as the chicken and coat with olive oil and salt and pepper. Thread the meat and vegetables on to the skewers.
Place the skewers onto a hot grill or under a hot broiler. Flip them once. You will know the skewers are ready to flip when they release from the grate with only a gentle pull. If you have to tug on them they are not ready to flip wait another minute.
Give the kebabs a drizzle of fresh lemon juice and dash of salt when they are done. Serve on their own or on top of a platter of rice or couscous.
If you are using wood skewers don't forget to soak them in water for at least 30 minutes to help stop them from burning.