Begin by preparing the marinade. In a bowl, combine chicken, olive oil, lemon juice, minced garlic, oregano, salt, and pepper. Cover and marinate in the fridge for at least 30 minutes.

Preheat your grill or skillet over medium heat. Cook the marinated chicken for about 6-8 minutes on each side, or until fully cooked. Let rest before slicing.

Prepare tzatziki by mixing Greek yogurt, grated cucumber, minced garlic, lemon juice, salt, dill, and olive oil. Stir until smooth and refrigerate.

Assemble gyros by placing sliced chicken in each pita, topping with tzatziki, cherry tomatoes, red onion, and parsley. Wrap tightly.

Serve immediately, preferably with a side of Greek salad or roasted potatoes.