Bell pepper
Bell pepper appears in 7 of the 123 recipes on Burgerman, roughly 6% of the library. In these builds it is the fresh element, and recipes here disagree about how much of it a burger can take. You will find it in Ribwich (The Simpsons), Sloppy Joe Smash Burgers and Duff Beer Sloppy Dog, among others. The highest-scoring recipe using it is Ribwich (The Simpsons) at 8.5 out of 10. It turns up most often alongside white onion, salt, black pepper.
