In a small bowl, whisk together the Greek yogurt, light ranch dressing, minced cilantro or parsley, and salt and pepper to taste until smooth.
Lay the flour tortillas flat on a clean work surface.
Divide the cooked chicken evenly among the tortillas, placing about 1/4 of the chicken on each.
Top the chicken with sliced avocado and tomato on each tortilla, and sprinkle with shredded cheese if using.
Drizzle a few tablespoons of the yogurt‑ranch sauce over the fillings on each wrap.
Roll each tortilla tightly around the fillings and secure with a toothpick if needed, then serve immediately.
