Preheat the oven to 400°F (200°C) and line a large baking sheet with parchment paper.
In a mixing bowl, toss the shredded chicken with the buffalo hot sauce until thoroughly coated.
Place the flatbreads on the prepared baking sheet and brush the edges with melted butter.
Spread the ranch or blue cheese dressing in an even layer across the flatbreads, leaving a small border for the crust.
Distribute the buffalo chicken and sliced red onions evenly over the dressing base.
Cover the toppings with a uniform layer of shredded mozzarella cheese.
Bake for 10 to 12 minutes until the cheese is melted and bubbling, and the edges of the flatbread are golden brown.
Remove from the oven and garnish with fresh green onions before slicing and serving.