Boil the chicken breast in lightly salted water until cooked through, let it cool, and cut into bite-sized cubes.
Soak the prunes in warm water for about 5 minutes to soften them. Then, cut them into small pieces.
Dice the cucumber and hard-boiled eggs. Coarsely chop the walnuts. Then, place the chicken cubes, prunes, cucumber, eggs, and walnuts in a large bowl.
In a small bowl, whisk together the mayonnaise and vinegar, and season with salt and pepper.
Pour the dressing over all the ingredients and mix thoroughly until the salad is evenly coated.
Serve the salad fresh or chill in the refrigerator for about 15 minutes. Enjoy!
