Place tofu, milk, soy sauce and nutritional yeast into food processor and blend until a smooth, thick paste forms, scraping bowl as needed.

Preheat oven to 350. Arrange shells on baking sheet.

Heat oil in medium skillet over medium heat. Add onion and sautee until softened, about five minutes.

Add garlic and spinach and continue to sautee until spinach wilts, about another minute.

Add tofu mixture and scallions and reduce heat to low. Cook, stirring frequently, until tofu softens and everything is evenly blended.

Spoon mixture evenly into shells. Bake for about 10 minutes, or until tops begin to brown.

Serve warm.