Bocadillo or bocata de atún is a classic variety of the Spanish bocadillo sandwich. It typically consists of nothing more than a Spanish-style baguette (barra de pan) which is sliced down the middle and filled with a generous amount of canned tuna in oil.
The bread’s interior may optionally be rubbed with tomato halves, olive oil, or both for added flavor. Apart from the tuna, other common additions to the sandwich’s filling include olives, onions, cheese, strips of fire-roasted piquillo peppers, slices of tomatoes or hardboiled eggs, anchovies, and alioli (garlic and mayonnaise sauce).