Wash the California grapes and cut them in half. Cut the celery in half lengthwise and then slice into thin slices. Roughly chop the walnuts.

(*Optional: add the walnuts to a hot pan over medium heat and toast them with a little salt for a few minutes, stirring frequently)

Add the tuna to a large bowl. Use a fork to flake the tuna and break apart any big pieces.

Add the California grapes, celery, and walnuts.

Add the lemon juice, mayo, Dijon mustard, dill, salt, and pepper. Mix well until everything is combined.