Drain and rinse the cannellini beans in a colander under cold water for about a minute. Shake off the excess water and pat dry with a towel.
Dice the cucumber and halve the cherry tomatoes. Thinly slice the red onion and halve the kalamata olives.
In a large mixing bowl, combine the beans, cucumber, tomatoes, red onion, and olives.
In a small bowl, whisk together the olive oil, lemon juice, minced garlic, and dried oregano until combined.
Pour the dressing over the salad and toss gently to coat everything evenly.
Add the feta cheese and chopped parsley, and toss once more, gently, so the feta doesn't break apart too much.
Season with salt and pepper, taste, and adjust as needed, keeping in mind the feta and olives already add plenty of salt.
Let the salad rest for 15 minutes at room temperature before serving so the beans can soak up the dressing.