Drain the canned tuna and the cannellini beans thoroughly to remove excess moisture.
In a small mixing bowl, whisk together the extra virgin olive oil, lemon juice, dried oregano, sea salt, and black pepper until well emulsified.
Dice the cucumber, halve the cherry tomatoes, finely mince the red onion, and roughly chop the fresh parsley and kalamata olives.
In a large bowl, combine the drained tuna, white beans, cucumber, tomatoes, onion, olives, and parsley.
Pour the lemon-herb dressing over the tuna mixture and toss gently with a spoon, keeping the tuna in large, satisfying chunks.
Arrange the fresh arugula in a serving bowl and top with the Mediterranean tuna and bean salad.