Mix together the water and cucumber slices. Refrigerate for 1 hour prior to serving. Serve over ice if desired.
Preheat a grill or grill pan on medium heat.
In a bowl, whisk together the ingredients for the marinade. Season with salt and pepper to taste. (Reserve some aside in a separate bowl for finishing so there is no cross contamination).
Cook the chicken: Brush one side of the chicken with the marinade and season with salt and pepper. Then place that side down on the grill or grill pan. Brush the top side with marinade and season with salt and pepper. Cook on one side until nicely marked for about 6 minutes then flip over and brush with marinade again. Cook to an internal temperature of 160 degrees for about 6 minutes more. While the chicken is cooking,
Once the chicken is cooked, set aside to rest for 2 to 3 minutes. Then dice into bite-sized pieces.
Warm the pita on both sides using a grill or grill pan.
Make the pita: Spread mayo on the inside of the pita. Layer with lettuce, tomato, chicken, and onion. Drizzle with reserved marinade.
Serve: enjoy the pita with pita chips, hummus, and cucumber water.