Run a sharp knife down the back of each prawn and remove the grey line that runs from the head to the tail. Whisk the coconut milk until smooth, then tip half into a bowl with the prawns. Add half the lime juice and a pinch of salt, mix well and set aside for 15 mins.
Meanwhile, mix the remaining coconut milk with the rest of the lime juice, the sesame oil, sugar or honey, and a pinch of salt.
Divide the watercress or spinach between two plates, then top with the mango, avocado and red onion slices, the mint and sliced chillies.
Pour a 1-2cm depth of oil into a large saucepan over a medium heat. Combine the desiccated coconut with the cornflour and some seasoning. Drain the prawns and turn in the cornflour mixture to coat, shaking off any excess.
Drop one prawn into the oil; if it sizzles, add a few more, but don’t overcrowd the pan. Fry for 1-2 mins on each side until crisp and golden, then transfer to a plate lined with kitchen paper. When all the prawns are fried, scatter them over the salad and drizzle with the dressing.