Cook pasta according to package directions. Drain and set aside for a few minutes.
To prepare roux, melt butter into a medium saucepan over medium heat. Once melted whisk in flour, salt and pepper. Stir and cook for 3-4 minutes until color of roux will gets slightly darker. Slowly whisk in milk, stirring continuously until thickened, about 2 minutes. Reduce heat to a simmer and stir in cheese until melted.
Transfer cooked pasta to large dutch oven or pot over low heat. Pour cheese sauce over top, stirring to combine.
Add green chilies, chicken, bacon and salsa verde, stirring to combine. This is a thick and creamy sauce. To thin sauce, add additional tablespoons of milk at a time until at desired consistency.
Notes
Watch Pasta Carefully. I like to undercook my pasta 1 minute less than the package recommends so that it stays al dente as it warms in the cheese sauce.
Rotisserie Chicken. To make prep work easy, use a rotisserie chicken, shredded in the mac and cheese. This way you don't have to cook your own chicken if you don't want to.
Splashes of Milk. To thin the mac and cheese sauce, add a few splashes of milk and stir. When mac and cheese sits in the pot, it tends to thicken up. The milk will help.