Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Make the buffalo chicken: In a medium bowl, combine the shredded chicken with hot sauce, melted butter, garlic powder, onion powder, smoked paprika, cayenne, salt, and pepper. Toss everything together until the chicken is well coated. Give it a taste and adjust the heat level to your liking.
Prep your flatbreads: Lay the flatbreads out on your prepared baking sheet. Spread a generous layer of ranch dressing over each one, going almost to the edges.
Layer it up: Sprinkle the mozzarella and cheddar cheeses evenly over each flatbread. Top with the buffalo chicken mixture, red onion slices, and a little extra mozzarella on top if you're feeling generous.
Bake: Pop the flatbreads into the oven and bake for 12–15 minutes, until the cheese is melted and bubbling and the edges of the flatbread are golden and crisp.
Finish and serve: Remove from the oven and immediately top with crumbled blue cheese, sliced celery, green onions, fresh parsley, and a drizzle of extra hot sauce. Slice and serve right away!