Prawn, coconut and cashew curry

Ingredients

• 2 tablespoons vegetable oil
• 1 finely sliced red onion
• 2 cloves, finely chopped garlic
• 2 cm, peeled, finely chopped ginger
• 1 finely sliced long green chilli
• 2 roughly chopped roma tomatoes
• 2 teaspoons garam masala
• 1 teaspoon ground turmeric
• 500 grams peeled, deveined, heads and tails on green prawns
• 400 millilitres can coconut milk
• 1/2 cup cashews, toasted
• 1 tablespoon tamarind paste
• coriander leaves, steamed
• basmati rice, lime wedges, to serve