The term 'oniony breakfast roll' refers to a type of bread roll known as a bialy. Bialys are a traditional Jewish food originating in the Polish city of Bialystok. They are made from a dough similar to that of a bagel, but instead of being boiled and then baked, they are simply baked. The dough is topped with onions, poppy seeds, and sometimes garlic. Bialys are usually served warm and are a popular accompaniment to breakfast dishes.