Grind coconut and cumin seeds into a smooth paste. Set aside.
In a pan, combine cucumber, green chilies, turmeric, salt and ½cup of water; bring to a boil and simmer till cucumber is tender, about 10~12 minutes.
Stir in the ground coconut mixture and cook for 3~4 minutes for the flavors to mingle. Taste and adjust the salt accordingly. Take off the heat.
In another small pan, heat the coconut oil, add mustard seeds and dry red chili. Once the seeds splutter, add curry leaves and onions. Cook for 3~4 minutes or until the onions are golden brown.
Add the onions to the curry along with the whisked yogurt, mix well. Serve with rice.