• Spray a 4-quart slow cooker with nonstick cooking spray and lay 2 pounds boneless skinless chicken breast on the bottom of it.
• In a small bowl combine 1 cup diced onion, 2 teaspoons minced garlic 1 teaspoon dried oregano, ½ teaspoon salt, ½ teaspoon ground black pepper, 3 tablespoons olive oil, 1 tablespoon red wine vinegar, 2 tablespoons lemon juice, and ⅓ cup water.
• Pour the onion mixture over the chicken and place the lid on the slow cooker. Cook on LOW for 6-8 hours, or on HIGH for 4-6 hours.

Tzatziki Sauce

• In a medium bowl combine 2 cups plain greek yogurt, 1 cup finely grated cucumber, 2 teaspoons minced garlic, 1 tablespoon white wine vinegar, 1 teaspoon dried dill , 1 teaspoon dried oregano, 2 tablespoons lemon juice, 1 tablespoon extra-virgin olive oil.
• Add salt, and ground black pepper, to taste. Cover the bowl and refrigerate for at least 30 minutes before serving to allow the flavors to meld.

For Serving

• Shred the chicken in the crockpot before serving with the tzatziki sauce, warm pita bread, diced red onion, shredded romaine lettuce, diced cucumber, and diced tomatoes.