Add the ground spices and the remaining ingredients (except the chicken and onion) into a blender and blend until smooth. Mix thoroughly with the chicken pieces in a bowl. Cover with film and marinate in the refrigerator for at least 6 hours or overnight.
Soak sufficient kebab sticks in water (allow for four chicken pieces per stick).
Thread the chicken onto the sticks leaving a gap between the pieces. Place on a grill tray with a little olive oil and scatter around the onions. Grill, turning the kebabs two or three times, for about 12 minutes or until the tikka is brown.
Serve with the onions, salad and rotis and/or naan.