Start by preparing the ingredients. Drain the can of tuna well. Rinse the white beans under cold running water and drain them thoroughly in a colander. Finely chop the half red onion, halve the cherry tomatoes, and chop the fresh parsley. Finally, juice the half lemon.
Take a large bowl and add the white beans to it. Add the drained tuna and gently break apart the larger fish pieces with a fork. Then add the chopped red onion, the halved tomatoes, and the chopped parsley. Gently toss all the ingredients together.
Pour the extra virgin olive oil and fresh lemon juice over the mixture. Season the salad further with a pinch of salt and some freshly ground pepper. Toss everything together once more, so the oil and acid distribute evenly over the salad.
Divide the salad directly onto plates or transfer it to a serving bowl. The salad is ready to eat immediately, but can also be stored in the refrigerator to allow the flavors to develop further.