The tofu turkey is what Marie made for Thanksgiving because she felt her family needed to eat healthier. She thought it was tasty, but the rest of the family didn't like it at all.
A special mold was needed to make the tofu into the shape of a turkey. Worcestershire and beet juice were also used to give it some color and flavor. As Ray mentioned, it kind of starts out with an aftertaste. And Debra replied that it had an "authentic" turkey flavor. And since it's not a real turkey, the family wouldn't fall asleep after dinner.
The tofu turkey was only seen in the Season 3 episode "No Fat".