This is a very common and simple South Indian curry, that goes well with rice
Cut the cucumber into small square pieces. Cook this along with a little water, salt and turmeric powder.
Meanwhile, grind together curd, grated coconut, green chillis, and cumin seeds.
Add th ground mixture to the cooked coconut, and heat it on a low flame for one or two minutes. Make sure that you stir the mixture continuously
Splutter mustard seeds in a pan, add red chillis and curry leaves to it. Add this to the cucumber, and mix well.