1. In a mixing bowl, combine Greek yogurt, olive oil, garlic, lemon juice, oregano, cumin, paprika, salt, and black pepper.
2. Add chicken strips to the marinade and mix well. Let it marinate for at least 30 minutes.
3. Preheat the grill to medium-high heat.
4. Grill the chicken strips for about 5-7 minutes on each side or until fully cooked.
5. Warm the pita bread on the grill for a minute on each side.
6. Assemble the gyros by placing grilled chicken strips on the pita bread, then top with tzatziki sauce, chopped tomatoes, sliced red onion, and shredded lettuce.
7. Serve immediately and enjoy!