Using your hands, crumble the tofu finely into a mixing bowl (or break into a few pieces, place in a food processor, and pulse on and off until finely and evenly chopped, then transfer to a mixing bowl).
Add the mayonnaise, celery, and optional scallion and nutritional yeast. Mix well.
Use as a spread for sandwiches—closed or open-faced, mound over greens, or just enjoy on its own on the side of salads or vegetable dishes.