In a pan boil the rice, drain and cool, either under cold water or, even better, by stirring ice cubes through it.
Once cold, stir in three tablespoons of extra-virgin olive oil.
Cut the apple and the cheese into cubes, cut the celery, complete with leaves, into rounds and crumble the walnuts.
Put all the ingredients into a bowl, stir in the rice and add oil as liked. It is a good idea to let the salad rest for a few hours before serving, to allow the flavours to blend.