Cheese and chicken bake

150g (60Z) cooked,chopped chicken
2 sticks of chopped small celery
1 small grated onion
4 tablespoons of natural yogurts
4 tablespoons of mayonaise
salt and pepper
25g (1 oz) crushed potato crisps
25g (1 oz) grated cheese

Mix together all the ingredients except the crisps and cheese,
place in 850 ml (1.5 pints) oven proof dish,
Mix the cheese and crisps and sprinkle over the top,
bake at gas setting 7 or 220'c for 20mins or until golden brown