In a large mixing bowl, combine the shredded chicken, Buffalo sauce, ranch dressing, and cooked pasta. Add garlic powder, green onions, diced celery, and half of both the sharp cheddar and mozzarella cheeses. Mix thoroughly.
Season the mixture with salt and pepper to taste.
In a separate bowl, mix the breadcrumbs with the remaining cheddar and mozzarella. Drizzle olive oil over the mixture and toss lightly.
Transfer the chicken and pasta mixture into a greased 9x13-inch casserole dish, spreading it evenly.
Sprinkle the breadcrumb and cheese mixture evenly over the top of the casserole.
Bake for 25-30 minutes, or until the top is golden brown and crispy.
Let the casserole cool for about 5 minutes before serving.
Notes
Garnish with extra chopped green onions and ranch dressing for added flavor.