In a large bowl, combine the beans, tuna, celery, parsley, shallot, and lemon zest. Season with salt and pepper.
Using a wooden spoon, gently break up the fish into small chunks and mash a few of the beans.
Juice half the lemon. Add the lemon juice, olive oil, and vinegar, then gently fold in the kale or arugula. Season with salt and pepper. If the salad is still a bit dry, drizzle a bit of the oil reserved from the tuna can.
Cover and refrigerate for 30 minutes or overnight