"'What's that?' said Ron, pointing at a large dish of some sort of shellfish stew that stood beside a large steak-and-kidney pudding. 'Bouillabaisse,' said Hermione"
(Goblet of Fire 251).
Bouillabaisse is, as Hermione goes on to say, a French dish which many find quite tasty. As a vegetarian (even before I was a vegetarian), I do not care to eat fish of any kind. While it is likely possible to create a vegetarian version of bouillabaisse, it would require creating so many subtly different flavors of seitan that I would be cooking for days.
However, if you do enjoy the flavors of seafood, I recommend that you give bouillabaisse a try. There is a promising looking recipe in The Unofficial Harry Potter Cookbook.