In a large pot of salted boiling water, cook the penne pasta according to package instructions until al dente. Drain and set aside.
In a large mixing bowl, combine the cooked shredded chicken with buffalo sauce and ranch dressing. Mix until the chicken is well coated.
Add the cooked penne pasta to the chicken mixture and stir until combined. Fold in half of the shredded cheddar and mozzarella cheeses, and season with salt and pepper.
Lightly grease a 9x13 inch baking dish. Pour the pasta mixture into the dish and spread it out evenly.
Sprinkle the remaining shredded cheddar and mozzarella on top. If using, mix breadcrumbs with olive oil and sprinkle over the cheese for a crunchy topping.
Place the baking dish in the preheated oven and bake for about 25-30 minutes or until the cheese is melted and bubbly.
Once baked, remove from the oven and sprinkle with chopped green onions for freshness.
Notes
Adjust the buffalo sauce to your preferred spice level.