In a bowl, combine olive oil, garlic powder, onion powder, smoked paprika, salt, and pepper.
Add sliced chicken breast to the marinade and coat thoroughly.
Cover and let the chicken marinate for at least 30 minutes.
Heat a grill or skillet over medium-high heat.
Cook the marinated chicken for about 5-7 minutes on each side until fully cooked.
Remove chicken from the heat and let it rest for a few minutes.
Warm the pita breads on the grill or in a pan.
Slice the cooked chicken into strips.
Assemble the gyros by placing lettuce, tomato, onion, and chicken in the pita.
Drizzle tzatziki sauce over the filling and wrap the pita tightly.