Slice the yellow onion thinly and place it evenly at the bottom of the slow cooker.

In a mixing bowl, combine minced garlic, chicken broth, olive oil, dried oregano, ground paprika, salt, and black pepper. Stir well to blend into a marinade.

Place the boneless, skinless chicken breasts on top of the onions in the slow cooker, then pour the mixed seasoning blend over the chicken.

Cover the slow cooker and cook on low for 6 to 8 hours or on high for 3 to 4 hours.

Once cooked, shred the chicken in the slow cooker using two forks and mix it with the onions and juices.

Fill warmed pita bread with the shredded chicken mixture, top with tzatziki sauce, diced tomatoes, cucumbers, and red onions.