In a bowl, combine the olive oil, minced garlic, dried oregano, dried thyme, salt, and pepper. Add the thinly sliced chicken thighs to the marinade, ensuring they are evenly coated. Cover and refrigerate for at least 30 minutes, or overnight for maximum flavor.
In a separate bowl, combine the Greek yogurt, grated cucumber, minced garlic, fresh lemon juice, chopped dill, salt, and pepper. Mix well and refrigerate until ready to use.
Heat a skillet or grill pan over medium-high heat. Once hot, add the marinated chicken slices in a single layer. Cook for 4-5 minutes on each side, or until the chicken is cooked through and nicely browned. Remove from heat and set aside.
Place frozen french fries in an air fryer that is preheated to 400F. Cook them for 12-15 minutes until hot and crispy.
Warm the pita bread or flatbreads according to package instructions. Spread a generous spoonful of tzatziki sauce onto each warmed bread. Top with slices of cooked chicken, followed by fries, sliced tomatoes, and red onions.