Combine all ingredients in a large ziplock bag, and massage the bag to coat the chicken. Marinate in the fridge for at least 4 hours (I prefer overnight).
Grill or bake the chicken in your preferred method until cooked through (165°F). Let rest on a cutting board for a few minutes, then shred the chicken.
In a small bowl, combine all ingredients. Place in a resealable plastic bag and set aside. This makes drizzling it on top of the pitas easier, but you can also just leave it in the bowl and spoon it on top.
Spread the hummus evenly across the top of each pita.
Sprinkle the diced cucumber evenly across the top of the hummus.
Cut a small corner of the bag full of tzatziki sauce and drizzle (or use a spoon) on top of each pizza. Garnish with a few cilantro leaves and enjoy!