1) Open the can of beans and pour it all in a large sieve or colander. Rinse the beans gently and then let them sit there for a couple of minutes until drained. Transfer them to a medium mixing bowl.
2) Drain the canned tuna and flake it up a bit using a fork. Then add the tuna to the beans in the bowl.
3) Chop the red onion into thin slices and add them together with the arugula salad to the bowl as well.
4) Stir all the ingredients until well combined. Then season with a little pinch of pepper and salt. Drizzle with the lemon juice (or vinegar). Add a good splash of the olive oil and the pink pepper.
5) Stir the salad well again. Then check the seasoning of the bean salad and add extra pepper, salt, lemon juice (or vinegar) or olive oil to taste if necessary. Place the salad in the fridge for another 10 minutes until chilled. Serve.