At its simplest, bocadillo de mejillones is a type of seafood bocadillo sandwich consisting of Spanish bread that’s filled with mussels. The mussels used for the filling are usually pickled (mejillones en escabeche), while the traditional choice of bread is a Spanish-style baguette called barra de pan.

Typically, the baguette is cut in half along the middle, topped with a layer of pickled mussels, and (optionally) drizzled with the pickling sauce or olive oil before it’s closed with the other half of the bread. The sandwich may occasionally be enhanced with the addition of other ingredients such as lettuce or arugula, tomato or cucumber slices, potato fries, queso fresco (fresh cheese), mayonnaise, and lemon juice.

This Spanish sandwich makes for an excellent afternoon snack or a light and nutritious lunch or dinner, and it is typically accompanied by a cold beer, a glass of orange juice, or a cup of coffee on the side.