Tuna bun is a Hong Kong-style pastry. It consists of dough that's filled with tuna fish, and usually mayonnaise and eggs, then shaped into a roll and baked. The tuna is usually of the canned variety, while the dough is typically made with a combination of flour, sugar, water, yeast, and milk.

Before baking, the bun is often brushed with sugar water in order to develop a nice glaze. These buns can be found in many Hong Kongese bakeries, but they're also often sold in Chinatown bakeries overseas.