Chop the rosemary and mix in a bowl with the lime zest, juice, olive oil, prawns and a pinch of salt and pepper. Stir well and set aside.
Chop the coriander and garlic and add to another bowl with some more olive oil. Quarter the mushrooms and add to this bowl. Season a little and stir in the chilli flakes.
Alternate the mushrooms and prawns on skewers and barbecue for about 8 to 10 minutes, until cooked through. Serve hot.