In a small pan over medium heat add the cucumber and enough water to cook it, starting with 1 tablespoon. Stir in the salt and finely diced green chili and cook until the cucumber is soft and the water is evaporated. This will take about 6 to 8 minutes
While the cucumber is cooking, using a small blender and grind the coconut, mustard and cumin seeds into a paste using 1 tablespoon of water. Add another tablespoon only as needed to process the ingredients.
After removing the cucumber from the heat, stir in the coconut paste so that the ground cumin and mustard seeds heat up slightly. Set aside for 10 minutes.
Stir in the yogurt and make the tadka.
Heat the oil in a small pan over medium heat. Test the oil with a couple of mustard seeds. When they spluttering, add the rest of the seeds and toast for 30 seconds. Add the red chili and curry leaves. Stir for another 30 seconds, then remove from the heat.
Pour seasonings over the raita and serve.
The make cucumber raita vegan, use a plant-based plain yogurt.