Season the chicken with salt and pepper and grill or bake until cooked through but juicy, with the juices no longer pink. This can be done on the grill for ~20 minutes or in the oven at 400F for ~20-25 minutes. Either way, the chicken is done when the internal thigh temperature reaches 165F. Set aside until chicken is cool enough to handle, then remove the meat and chop.
Bring a large pot of water to a boil.
Meanwhile, make the green chili cheese sauce: whisk the butter and flour together in a large sauce pan over medium-high heat until smooth and bubbly. Once bubbly, cook ~1-2 minutes to form a roux. Slowly whisk in the milk and cook, stirring constantly, until milk is very warm and just starting to give off a bit of steam. Remove from the heat and whisk in 2 cups shredded cheese and sour cream until smooth. Add 1 teaspoon of salt. Stir in the green chilies. Taste for seasoning and add more salt if necessary (I'm a heavy salter).
Add a handful of salt to the boiling water. Add the pasta and cook according to package directions to al dente. Drain and add to the green chili cheese sauce. Pour all into a large casserole dish (I used a lasagna dish). Top with the remaining 2 cups shredded cheese.
In a small bowl, stir together the panko bread crumbs, parmesan cheese, and olive oil. Sprinkle over top the casserole. Bake at 350F for 30 minutes until warmed, golden, and bubbly. Garnish with a little fresh chopped parsley.