What do you put in the bread crumbs for the tuna salad filler?

You don't. Tuna salad is usually made of tuna, mayonnaise, and any vegetables or seasoning you want to add. I usually add a can of mixed vegetables (rinsed), a medium size finely chopped onion, a can of crushed pineApple (drained), and a little ground black pepper. Also, it usually tastes better the next day after all the flavors get to know each other.