Slice the yellow onion into thin rings and place them in the bottom of the slow cooker.

In a medium bowl, combine minced garlic, chicken broth, olive oil, dried oregano, ground paprika, salt, and black pepper. Whisk until well blended.

Lay the chicken breasts on top of the onions and pour the garlic mixture evenly over them.

Cover and cook on low for 6 to 8 hours or on high for 3 to 4 hours until the internal temperature reaches 165°F.

Remove the chicken using two forks and shred it, mixing it with the cooked onions and broth.

Warm the pita bread and spoon the shredded chicken mixture onto it, topping with tzatziki sauce, tomatoes, cucumbers, and red onions.