Photograph: Keiko Oihawa
Put four tablespoons of the yogurt in a bowl and put to one side. For the dip, whiz together the lime zest, reamining yogurt and mint leaves in a food processor until the mint is finely chopped. Add 1 tablespoon of cold water, season to taste and whiz again briefly. Tip into a serving bowl, cover and chill.
For the marinade, mix together the 4 tablespoons of Greek yogurt you put to one side with the ginger, paprika, garam masala and lime juice; season.
Prepare your prawns by making a small incision down the length of each prawn; if necessary, pull away and discard the black digestive cord. Rinse the prawns and pat dry. Thread on to skewers. Transfer to a shallow dish and coat thoroughly in the marinade. Cover and chill for 30 minutes.
Place a small frying pan over a medium heat. Add the nigella seeds and toast lightly for 1 minute or until they release a lovely smell. Sprinkle over the dip.
Preheat a griddle pan or grill to high. Wipe off the excess marinade from the prawn brochettes and brush with the oil. Place on the griddle pan or under the grill for 4-6 minutes, turning, until they are pink and cooked through. Cut the limes into lime cheeks and arrange with the cucumber batons on a platter. Scatter with mint leaves and serve with the bowl of dip.
Kitchen secret: soak wooden skewers in cold water for 30 minutes before using.