Slice the onion and place it at the bottom of the slow cooker.
In a small bowl, combine the minced garlic, chicken broth, olive oil, oregano, paprika, salt, and black pepper.
Place the chicken breasts on top of the sliced onions.
Pour the seasoning mixture over the chicken, ensuring an even coating.
Cover and cook on low for 6 to 8 hours or on high for 3 to 4 hours until the chicken is tender and easy to shred.
Shred the chicken using two forks and mix it well with the onions and juices in the slow cooker.
Serve the shredded chicken in warmed pita bread.
Top with tzatziki sauce, diced tomatoes, sliced cucumbers, and red onions and serve immediately.