You can make this pizza easily using frozen seafood mix and canned tuna. You can also use canned white sauce, but we only need a little, so let's make it from scratch.
Enjoy the white sauce, which makes it taste like a gratin.
It's okay if the white sauce is somewhat lumpy (it's just a pizza!).I guess the tip is to wipe off any moisture from the ingredients with a paper towel?
Enjoy Japanese food around the world.