Preheat oven to 375°F. Then boil the Rotini and cook for a few minute less than al dente, or refer to package for the cooking time. Prepare the rest of the casserole as the pasta cooks.
Season the cubed chicken together with ½ tsp Italian seasoning, ¼ tsp pepper, also ⅓ tsp garlic salt.
Heat 1 tbsp olive oil in a skillet over medium-high-heat. Then add the chicken and sear, tossing occasionally for 4 minutes.
Add the broccoli then cook for 3-5 minutes. Remove from heat.
In a small bowl, combine the cream of mushroom soup, milk, 2-cups sharp cheddar cheese and sour cream. Then add the cooked broccoli and chicken.
Drain the pasta and mix it with all the casserole ingredients.
Lightly grease a 9 x1" casserole dish then add the casserole filling and top with 1 cup regular cheddar-cheese. Cover and bake for 20 minutes.
Then remove the cover and top with crispy fried onions and bake for another 8 minutes. Serve and enjoy!