Grate the cucumber and squeeze out excess moisture using a paper towel.

In a mixing bowl, combine the squeezed cucumber, Greek yogurt, fresh dill, lemon juice, and minced garlic. Season with salt and pepper, and mix until smooth.

Shred the rotisserie chicken and add it to the tzatziki sauce along with the diced red onion. Fold gently until chicken is coated.

Serve the salad chilled, with options like pita bread or on a bed of lettuce.