Peel the onion and cut it into thin rings, or wash, trim, and slice the spring onions. Wash and trim the celery, and cut into 1/2 in (1 cm) lengths. Wash the grapes and drain well. Roughly chop the walnuts. Wash the apples, cut into quarters, and remove the cores, slice thinly, and place in a bowl. Peel, core and thinly slice the pear, and mix with the apple. Stir in the lemon juice and mix thoroughly to coat the fruit to stop it browning.
Add the onion, celery, grapes and walnuts to the fruit. Pour over the vinaigrette dressing and toss lightly. Cover with cling film and chill in the fridge until needed.