This one could be embellished many ways, but I usually keep it simple. Serve it on a lettuce leaf, and you've got an easy, healthy lunch.
Tuna and white bean salad
1 5 oz can solid white albacore tuna in water, drained
1 15 oz can cannellini beans, drained and rinsed
1/2 small red onion, diced
3 T olive oil
3 T red wine vinegar
salt and pepper
In a medium bowl, break tuna into bite-sized pieces and stir in beans and onion. Add olive oil and vinegar and mix well. Season with salt and pepper to taste.