Place chicken in a saucepan; add water to cover. Bring to a boil over high heat, then reduce heat to medium-low, cover, and simmer until chicken is tender and no longer pink in the center, about 15 minutes. Remove chicken, let cool, and shred or cut into bite size pieces.
Combine the chicken, red onion, cucumber, garlic, and ranch dressing in a large bowl. Season with pepper to taste.