You can prepare this sweaty and delicious salad as a quick and simple meal. It is rich in protein, but also omega-3 fatty acids.
Drain the tuna from the oil, and rinse the beans under running water and drain it.
Chop the onion into thin slices, chop the lettuce as desired and mix the beans, the tuna and the onion in a serving bowl.
Drain the lemon juice, mix it with olive oil and pour the salad. Stir and season with salt and pepper.
Enjoy your salad.