HEAT THE OIL in a frying pan over a high heat. Meanwhile, score the fat on the duck breasts and season both sides with salt. Carefully put the duck in the hot pan, skin-side down, and reduce the heat to medium. Cook for 8–10 minutes until the skin is really crispy.
WHILE THE DUCK COOKS, peel the watermelon and cut it into bite-sized pieces, removing any obvious pips as you go. Chuck the watermelon into a large mixing bowl and leave to one side.
TURN THE CRISPY DUCK over and cook for another 8–10 minutes until beautifully tender and pink in the centre, then remove from the heat.
DESEED AND FINELY SLICE THE CHILLI while the duck finishes cooking. Put it in the mixing bowl with the melon and squeeze over the juice from the lime.
POUR OUT ANY EXCESS FAT from the cooked duck. Add the hoisin sauce, soy sauce and Chinese five-spice powder to the pan, and mix well. Remove the duck breasts from the pan, slice them into thick pieces and leave to one side. Put the watercress, mint and cashew nuts in the bowl with the watermelon, then toss everything together. Serve the salad with the beautiful duck slices, with the juices from the pan spooned over.