no grapes in the tuna! try olives instead.
no mayo/no relish, but fresh dill would work. you don't wanna make a chopped up gringo paste/mush for this. what i'm saying is some sort of salade nicoise.
that one has anchovies too. not sure if you ike them (i do)
this is with white bean which is italian
but works great with garbanzo too (in this case no potato--you have starch in bean)
just pare down to the basic notion + rebuild at will. vivan los mongrels.