Step 1: Make the Tzatziki Sauce
This should be done first to allow the flavors to meld. Grate the cucumber onto a clean kitchen towel. Gather the towel and squeeze firmly to remove as much liquid as possible. This is the most important step! In a medium bowl, combine the strained cucumber, Greek yogurt, minced garlic, lemon juice, fresh dill, and olive oil. Stir until well combined. Season with salt and pepper to taste. Cover and refrigerate for at least 30 minutes (or up to 2 days) to let the flavors develop.

Step 2: Prepare and Marinate the Chicken
In a large bowl or a zip-top bag, combine all the marinade ingredients: olive oil, lemon juice, red wine vinegar, minced garlic, oregano, salt, and pepper. Whisk until well combined. Add the cubed chicken to the marinade and toss to ensure every piece is thoroughly coated. Cover the bowl or seal the bag and let it marinate in the refrigerator for at least 30 minutes, but ideally for 2-4 hours. Do not marinate for more than 4 hours if using chicken breast, as the acid can start to break down the meat’s texture.

Step 3: Skewer the Chicken
While the chicken is marinating, prepare your skewers. If using wooden skewers, make sure they are soaking in water. Once the chicken has marinated, thread the pieces onto the skewers, leaving a small amount of space between each piece to ensure even cooking. Don’t pack them too tightly.

Step 4: Prepare the Grill
Preheat your gas or charcoal grill to medium-high heat (about 400-450°F / 200-230°C). Clean the grill grates thoroughly and brush them with oil to prevent the chicken from sticking.

Step 5: Grill the Chicken Souvlaki
Place the chicken skewers on the hot grill. Cook for about 8-12 minutes, turning the skewers every 2-3 minutes, until the chicken is cooked through and has a beautiful char on all sides. The internal temperature of the chicken should reach 165°F (74°C).

Step 6: Rest the Chicken
Remove the skewers from the grill and transfer them to a platter. Tent them loosely with foil and let the chicken rest for 5 minutes. This crucial step allows the juices to redistribute throughout the meat, ensuring it is moist and tender.

Step 7: Warm the Pitas and Assemble
While the chicken is resting, place the pita breads on the grill for about 30-60 seconds per side, until they are warm and pliable. To assemble, lay a warm pita flat, spread a generous layer of tzatziki sauce down the middle, slide the chicken off one or two skewers onto the pita, and top with halved cherry tomatoes, sliced red onion, and any other desired toppings. Fold and enjoy immediately.