1. In a mixing bowl, combine olive oil, oregano, garlic powder, paprika, salt, and black pepper.
2. Add chicken strips to the bowl and coat them well with the marinade. Let it sit for 15 minutes.
3. Heat a grill pan over medium-high heat. Grill the chicken strips until fully cooked, about 5-7 minutes per side.
4. Warm the pita bread on the grill pan for about 1 minute per side.
5. Assemble the gyros by placing grilled chicken strips on the pita bread, then top with tzatziki sauce, shredded lettuce, diced tomatoes, and sliced red onion.