In a large bowl combine beans, tuna, arugula, red onion, and parsley.
For dressing, in a screw-top jar combine vinegar, oil, oregano, salt, and pepper. Shake well to combine.
Pour dressing over tuna mixture; toss gently to combine. Squeeze juice from half of a lemon over salad. Serve with toasted gluten free bread, Crunchmaster sea salt crackers or an Udi's gluten free wrap.