Put the slices of banana into a solution of water, salt and turmeric and let sit for 5 minutes.Give it a good mix and transfer to a colander to drain completely.In a medium sized kadai on high heat, heat the oil.When it starts smoking, add the slices in small batches.Fry until golden and transfer onto a paper napkin.Repeat with the rest of the slices.Sprinkle with salt and chilli powder and let it cool.Store in an air-tight container for up to a week.