In a small bowl, combine mayonnaise, white grape juice vinegar, minced garlic, salt, and black pepper. Mix until smooth and creamy.
In a large mixing bowl, add cooked chicken breast and pour the prepared dressing over it. Gently fold until coated. Add diced cucumber, finely diced red bell pepper, and finely diced red onion. Stir until combined.
Cover the bowl with plastic wrap or a lid and refrigerate for at least 30 minutes to allow flavors to meld.
Garnish with fresh herbs like parsley or dill before serving. Enjoy on its own, in a croissant, or over lettuce.