Wash the arbi thoroughly and place in a pan or pressure cooker with enough water to cover it
Cook until they are soft (if using pressure cooker, 1-2 whistles or 15 minutes should be sufficient)
Let it cool and peel the skin off
Mash with a potato masher or fork without any lumps
Grind the green chilli with ginger and garlic to a coarse paste. You can also use a mortar and pestle for this
Place the mashed arbi in a bowl and add the chilli ginger garlic paste, chilli powder (if using), cumin powder, garam masala, and some salt
Mix thoroughly with a fork or your fingertips. The mixture will be quite sticky
Add the rice flour or cornflour to make the mixture more easy to shape and handle. You may need more or less flour than what I've mentioned above
Once the mixture comes together, shape into 3" discs on the palm of your hands and set aside
Heat oil in a small pan to shallow fry the arbi tikki
Once hot, place each tikki gently into the hot oil and fry both sides until golden brown
Drain on paper towels to absorb excess oil
Serve hot with ketchup or green chutney as a snack or appetiser