Preheat the oven to 350 degrees. Spray 9x13 casserole with non stick cooking spray, set aside.
Cook pasta to al dente, drain well. Toss in 1 tablespoon butter and ½ teaspoon garlic salt.
Add both cans of soup and evaporated milk to the large stockpot the pasta was cooked in. (You could use a large bowl, but why dirty another pan?) Whisk to combine.
Add the cooked, diced chicken, canned mushrooms (with liquid), cooked pasta, and half the shredded cheese. Stir to combine. Spoon the mixture into the prepared casserole dish. Top with the remaining cheese.
Melt 1 tablespoon butter. Mix with the panko bread crumbs. Sprinkle over the casserole.
Bake in preheated oven for 25-30 minutes or until hot and bubbly. Place under the broiler for a minute or two (watch carefully!) until the top is golden brown.
Notes
Garnish this amazing casserole with chopped parsley, thyme, kosher salt, or fresh ground black pepper.