Put the onion and oil into a small pan. Fry gently until the onion is soft and translucent. When the onion is cooked add the curry powder and continue to cook, stirring constantly, for one more minute. Remove from the heat and allow to cool.
Mix together the yogurt, mayonnaise, mango chutney and tomato puree. Stir in the cooled onion mixture. Season to taste.
Chop the chicken into bite sized pieces and stir into the dressing.
Refrigerate until ready to eat.
*I find that 900g cooked chicken drumsticks gives me 500g meat.