Spray the slow cooker with nonstick cooking spray to prevent sticking.

Place the boneless, skinless chicken breasts inside the slow cooker.

In a mixing bowl, combine the minced garlic, fresh lemon juice, diced onion, water, olive oil, red wine vinegar, oregano, allspice, and lemon pepper.

Pour this mixture over the chicken breasts.

Cover the slow cooker and set it to HIGH for 3-4 hours or LOW for 6-8 hours.

While the chicken cooks, prepare the Tzatziki sauce. In another bowl, mix the Greek yogurt, minced garlic, grated cucumber, chopped parsley, and salt. Cover and refrigerate for at least one hour.

Once the chicken is cooked, use two forks to shred the meat within the slow cooker.

Serve the shredded chicken with warm pocketless pita bread, diced tomatoes, sliced onions, sliced cucumbers, lettuce, and the prepared Tzatziki sauce.