In a large mixing bowl, open the cans of tuna packed in olive oil. Carefully drain the excess oil, then use a fork to flake the tuna into bite-sized pieces. This should take about 2 minutes.

Add the rinsed cannellini beans, chopped red onion, and freshly chopped parsley to the bowl with the flaked tuna. Gently fold everything together with a spatula, ensuring you maintain the integrity of the beans.

In a separate small bowl, whisk together freshly squeezed lemon juice, high-quality olive oil, Dijon mustard, and dried oregano for about 1-2 minutes until fully emulsified.

Pour the prepared vinaigrette over the tuna and bean mixture in the large bowl. Carefully toss the ingredients together using a spoon or spatula to ensure everything is well-coated.

Once combined, taste a small spoonful and season with salt and black pepper according to your preference.

Serve the salad immediately or refrigerate it in an airtight container for up to 2-3 days.