In a bowl, combine the minced garlic, lemon juice, olive oil, dried oregano, salt, and pepper.
Add the thinly sliced chicken to the marinade. Make sure the chicken is well coated. Marinate for at least 30 minutes or up to 2 hours in the refrigerator.
Cook the Chicken:
Heat a grill pan or skillet over medium-high heat. Cook the marinated chicken slices for about 5-7 minutes per side, or until fully cooked and nicely browned. Remove from heat and let rest for a few minutes.
Prepare the Gyros:
Warm the pita bread or flatbreads according to package instructions.
Spread a generous amount of tzatziki sauce over each pita bread.
Layer the cooked chicken slices, sliced tomatoes, cucumbers, and red onions on top of the tzatziki sauce.
Sprinkle with fresh parsley or dill and crumbled feta cheese, if desired.
Serve:
Roll up the pita bread around the filling to form a gyro. You can wrap it in foil or parchment paper to hold it together.
Serve immediately and enjoy your delicious Greek Chicken Gyros!