In a bowl mix together potatoes, green chilli-ginger paste, salt and cornflour and mix well. Set aside.
Heat one tablespoon oil in a non stick pan add garlic, mushrooms, red chilli powder, chaat masala, coriander leaves and sauté till mushrooms are cooked.
Add grated cheese and remove from heat and set aside. Divide the potato mixture and the mushroom mixture into eight portions each. Grease your palm slightly with little oil and spread out a portion of the potato mixture.
Place a portion of the mushroom mixture in the centre, gather the edges, seal and shape them into round tikkis. Heat a little oil on a non stick tawa and shallow fry the tikkis on both sides till golden.
Drain on absorbent paper. Serve with green chutney or lemon pickle.