In a large bowl, whisk together plain Greek yogurt, fresh lemon juice, minced garlic, and all the spices until well combined. Add the bone-in, skinless chicken thighs to the marinade, making sure they are evenly coated. Cover the bowl with plastic wrap and refrigerate for at least 4 hours or overnight for maximum flavor.

While the chicken is marinating, slice the onion into thin rounds and layer them at the bottom of your slow cooker. Spread the onion evenly, creating a bed that will hold the chicken above the juices.

Once marinated, remove the chicken from the refrigerator and place it on top of the sliced onions in the slow cooker. Cover with the lid and set the slow cooker to high for 3-4 hours or low for 4-6 hours.

After the cooking time, carefully remove the chicken thighs from the slow cooker and shred them into bite-sized pieces using two forks.

In a small bowl, combine one cup of Greek yogurt with any additional yogurt sauce ingredients you prefer. Mix until well blended and smooth.

To serve, warm up the pita bread, layer the shredded chicken onto the pita, drizzle generously with the yogurt sauce, and top with fresh vegetables.