Halve the melon and discard the seeds. Scoop out the flesh using a melon baller or peel and cut into bite-sized pieces. Cut off the peel and pith from the grapefruit and divide into segments, catching any juice that runs out in a bowl.
Slice the cucumber, halve the cherry tomatoes and pick over the watercress discarding any yellow leaves or coarse stalks. Keep the prepared ingredients in a bowl covered with cling film until required.
Heat the oil in a heavy non-stick frying pan and fry the turkey strips over a brisk heat for 5 minutes or until lightly browned and cooked through.
Whisk the dressing ingredients into the reserved grapefruit juice. As soon as the turkey is cooked, drain it from the pan and add to the bowl. Set aside to cool.
Divide the melon, grapefruit, cucumber, cherry tomatoes and watercress between serving dishes and spoon over the turkey and dressing. Toss lightly and serve.
Tip: The secret of successful stir-frying is to keep the heat under the pan high and the ingredients moving. This way the turkey seals quickly, trapping all the juices and flavour inside without the meat burning and sticking to the bottom of the pan