Preheat the oven to 375F. Lightly grease an 8-inch casserole dish.
In a large mixing bowl, stir together the cream cheese, buffalo sauce, and ranch dressing until smooth.
Add the chicken, ½ cup of mozzarella cheese, and cooked pasta. Mix to combine. Pour into the prepared casserole dish. Top with remaining mozzarella cheese and cheddar.
Bake for 18-20 minutes or until the cheese is melted and bubbly. Sprinkle with the chopped green onion to garnish. Serve immediately.