Cook the potatoes in plenty of boiling salted water for about 8-12 minutes until tender. Drain well and allow to cool.
In a bowl mix together the cooked potatoes, chick peas, onion, tomatoes and coriander. Add the lemon juice, chaat and chilli to taste. Season with salt and pepper- the salad should be quite highly seasoned.
Top with the Bombay Mix, Sev or peanuts if using, and finally with yoghurt.