01 - Combine olive oil, garlic, lemon juice and zest, oregano, thyme, cumin, paprika, salt, and pepper in a small bowl. Mix thoroughly.
02 - Place chicken in the crockpot. Rub spice mixture evenly over all pieces.
03 - Arrange sliced red onion and bell pepper on top of chicken. Pour chicken broth around the base of the crockpot, avoiding direct pouring over seasoned meat.
04 - Cover and cook on high for 4 hours or low for 6 to 8 hours until chicken is tender and easily shreds with a fork.
05 - Remove chicken from crockpot and shred using two forks. Return shredded meat to the pot and mix thoroughly with vegetables and cooking juices.
06 - Combine Greek yogurt, grated cucumber, garlic, dill, lemon juice, olive oil, salt, and pepper in a medium bowl. Mix well and adjust seasoning to taste. Refrigerate until ready to serve.
07 - Heat pita breads in a dry skillet over medium heat for 30 seconds per side or in a 350°F oven for 3 to 5 minutes until warmed through.
08 - Fill each warmed pita with shredded chicken mixture, lettuce, tomatoes, red onion, feta cheese, and olives. Spoon tzatziki generously over filling. Fold and serve immediately.