Toasted baguette with mentaiko (marinated pollock roe). 明太子フランス。A type of sozai-pan, buns with savory fillings ("sozai" is the term for the side dishes eaten with rice).
Bread with mentaiko is an unexpected, but excellent combination. The marinated pollock roe is made into a paste that is then spread inside on the bread. Finally, the bread is lightly toasted. For bread, usually a baguette is used. Like Yakisoba-pan, this is a great Japanese invention (mentaiko-furansu is more upscale).
By the way, mentaiko is also used as flavoring for a delicious spaghetti dish.
Available in bakery shops.