Bring a large pot of salted water to a boil. Add 8 ounces of penne or rigatoni and cook according to package instructions until al dente. Drain and set aside.
In a large bowl, combine 1 pound of cooked, shredded chicken breast with 1 cup buffalo sauce and 1 cup ranch dressing. Toss until the chicken is evenly coated with the flavorful sauce blend.
Add the cooked pasta to the chicken mixture. Stir in 2 cups shredded cheddar cheese and 1 cup shredded mozzarella cheese until everything is well combined.
Transfer the cheesy buffalo chicken pasta mixture into a greased 9x13-inch baking dish. Sprinkle 1/2 cup diced green onions evenly over the top.
In a skillet, heat 1 tablespoon olive oil over medium heat. Add 1/2 cup breadcrumbs and toast until golden brown and crisp, about 3-5 minutes. Remove from heat.
Sprinkle the toasted breadcrumbs evenly over the pasta bake. Bake at 350°F (175°C) for 20-25 minutes, or until the cheese is bubbly and the topping is golden.
Remove from the oven and let cool slightly before serving. Garnish with extra green onions if desired, and dig in!