When we eat a tuna fish sandwich (or a salmon sandwich), we make it the usual way. We mix tuna fish with miracle whip something similar. But I found that if I add diced vegetables to the sandwich, it's super tasty and my kids eat their veggies without a single complaint.
In this photo, I mixed red bell peppers and cucumbers into our sandwiches. But I've also used green peppers, celery, and carrots. I have hopes to add zucchini and cherry tomatoes this summer, but we'll see how well the garden cooperates.