Remove and discard the watery seeds from the cucumber then dice.
Combine the cucumber with the ground cumin, lemon juice, ¾ of the spring onion and mint (holding back the rest for garnish), and 1 tbsp of the mustard oil. Season with salt and pepper.
Tip this onto a shallow serving bowl and smooth out. Garnish with the remaining spring onion and mint, and the cumin seeds - then a final drizzle of mustard oil (if using).
Serve right away or refrigerate until needed.
Notes
Serve: Serve alongside Indian meals as a cooling side dish to balance rich or spicy flavours. It works well with both meat and vegetarian dishes and can also be used as a simple dip.Fridge: Raita can be made ahead and will keep for 2–3 days in the fridge. It may release some liquid as it sits — simply pour this off and stir before serving.Freezer: Freezing is not recommended. Raita is best enjoyed fresh.