Heat a medium saucepan over medium heat, add the butter and allow it to melt. Add the onion and the garlic and sauté, stirring occasionally, until soft and translucent, about 10 minutes. Add the cayenne, paprika and Cajun seasoning and stir to combine.

Whisk in the flour and let cook, continuing to whisk frequently until the mixture is golden brown. Add the milk, whisking to combine. Cook, stirring occasionally until the mixture has thickened, about 5 minutes. Slowly whisk in the Parmesan, provolone and mozzarella until completely combined. Season to taste with salt and keep warm over low heat.

Set aside ½ cup of the crawfish. In a blender combine the  remaining crawfish with ¼ cup of the seafood stock and pulse until the crawfish is minced but not pureed. Stir in the crawfish mixture into the cheese sauce.

Bring a large pot with the remaining seafood stock and water to the boil; salt the water and bring back to a boil. Pour in the pasta and cook, stirring occasionally, until al dente, about 10 minutes. Before draining, set aside about one cup of the cooking water.

Drain and return the pasta to the pot. Add the sauce and stir to combine and evenly coat the noodles with the sauce. If the sauce begins to get too clumpy, add some of the reserved pasta water, a tablespoon at a time.

To serve, ladle into warm pasta bowls and top with the remaining crawfish, green onions and parsley.