Marinate chicken in a mixture of tandoori paste, cumin, lemon juice, two-thirds of the yoghurt and two-thirds of the garlic for at least 3 hours.
Preheat oven to 180c. Line 2 baking trays with baking paper and thread chicken pieces onto skewers (soak skewers in water for 30 mins to prevent burning).
Heat oil in non-stick frypan to medium and saute onion until soft, then transfer to one of the baking trays.
Increase heat of frying pan and cook chicken skewers for 2 minutes one side and 1 minute the other side. Transfer these to the second baking tray and bake for 6-8 minutes. Put onion into oven for final 2 minutes of cooking time.
Meanwhile, bring water to simmer in a large saucepan. Add spinach and cook, stirring gently, until limp. Add the remaining garlic and stir to combine.
Toss coriander and warm onion to combine.
Serve wilted spinach topped with onion mixture and chicken skewers, and offer lemon wedges, chutney and remaining yoghurt.