Preheat the oven to 350F and grease a 9x13 pan with nonstick cooking spray. 

Bring a large pot of salted water to a boil. Cook the cavatappi noodles to al dente according to the package directions (about 10 minutes). Then drain the noodles and run them under cold water to stop the cooking process. Drizzle the noodles with 1 tablespoon of olive oil so they don’t stick together while you make the sauce. 

Add the remaining two tablespoons of olive oil to a large high sided pot or skillet set over medium heat. When the oil is hot, add the onion and saute under tender– about 5 minutes. 

Next, add the garlic and butter. Stir until the butter has fully melted. 

Sprinkle the flour over the onions and then whisk to form a thin paste. Cook the roux for 1 minute, stirring constantly. 

Slowly whisk in the milk (make sure to keep stirring), heavy cream, hot sauce, and ranch seasoning. 

Cook the sauce for 5 minutes, or until it is bubbling and slightly thickened. Next, add 2 cups of cheddar cheese and 1 cup of monterey jack cheese. Stir until the cheese has fully melted. Taste and season with salt and pepper, if needed. 

Remove the pan from the heat and add the chicken and cooked pasta. Stir to combine. 

Transfer the pasta to the prepared baking dish and sprinkle over the remaining 1 cup cheddar cheese and 1 cup monterey jack cheese. Bake uncovered for 20 minutes or until the cheeses are melted and bubbling. 

Sprinkle over the blue cheese crumbles and green onion, and serve immediately.