Put the cauliflower florets and the finely chopped celery raw in the food processor, quarter the onion and add the garlic clove. Let the food processor run until it is a crumbly mass. Add the remaining ingredients to the mixture in the machine and turn on until it is somewhat mixed. Transfer to a bowl and knead again by hand. If the mixture is still too wet, add breadcrumbs accordingly.
Shape the schnitzel from the mixture, turn in breadcrumbs and fry in hot oil.