Marinate the chicken slices in olive oil, lemon juice, oregano, salt, and pepper for at least 30 minutes.
Preheat your grill or skillet over medium-high heat.
Grill the marinated chicken for 5-7 minutes on each side until fully cooked and golden brown.
Prepare the veggies: chop the cucumber, tomatoes, and onion.
Warm the pita bread on the grill for about 1 minute on each side.
Once the chicken is done, let it rest for a few minutes before slicing it into strips.
Assemble the gyros by placing chicken on the warmed pita.
Top with diced cucumber, tomatoes, onions, and a generous drizzle of tzatziki sauce.
Fold the pita around the filling to create a wrap.
Serve immediately with lemon wedges and enjoy!