In a big bowl, place the diced cucumber and coconut.
Heat the oil in a small pan. Temper the mustard and cumin seeds, curry leaves, chillies and add the asafoetida towards the end, just after you switch off the flame. Transfer this tempering over the cucumbers.
Add the salt, coriander and toss well, adding the lemon or yogurt if using.
Serve immediately or refrigerate, adding the peanuts and tossing well just before serving, so that they remain crunchy.
Serve with poLi/roti and vegetable curry or eat as it is as a snack time salad.