that was purposefully written by mr krabs as a prank I don’t recall there actually being any plankton in the recipe.
actually now that I recall, the creators of the show were interviewed on the question and they said that (canonically) there was no meat based ingredient inside of the patty.
I feel like we should be more focused on what the secret ingredient is tbh
anyone can put a patty on a bun, with lettuce, cheese, onions, tomatoes, ketchup, mustard, pickles, and top bun in that order, but the secret ingredient seems to be the key here.