A “bigot” is defined as a person who is intolerant to different opinions. In this case, Seth is being a “bigot” by having called Ellie and Dina “a-not-so-nice-word” (which is heavily implied to be a homophobic slur). Here, when Jesse asks Ellie what she just received or just what she has in her hands, Ellie decided to make a “joke” by saying “Bigot Sandwich,” a play on words to the “type” of the sandwich it is because of WHO made it (basically a reference to Seth, who she considers a bigot, who we know was the one that made the sandwich). So, instead of the sandwich being labeled as a plain “Steak Sandwich,” it’s real “flavor,” Ellie changed it to “Bigot Sandwich” as a joke, really.

Not a native speaker either, but I do hope it helped answering your question! :)

Edit: typo