Preheat Oven and Prepare Pasta: Preheat your oven to 350°F (175°C). Cook the rotini pasta according to package directions until al dente. Drain and set aside.

Cook Chicken: In a large skillet, heat olive oil over medium heat. Add diced chicken, Italian seasoning, garlic salt, and pepper. Cook until the chicken is fully cooked and slightly golden, about 7-8 minutes. Remove from heat.

Steam Broccoli: While the chicken cooks, steam the broccoli florets until tender-crisp, about 4-5 minutes. You can do this in the microwave or on the stovetop.

Mix Sauce: In a large bowl, combine the condensed soup, sour cream, and milk. Stir until smooth and creamy.

Combine Ingredients: Add the cooked chicken, steamed broccoli, cooked rotini, and 1 ½ cups of the shredded cheeses to the sauce mixture. Stir until everything is well coated.

Transfer to Baking Dish: Pour the mixture into a greased 9×13-inch casserole dish, spreading evenly.

Top and Bake: Sprinkle the remaining 1 ½ cups of cheese over the casserole. Then evenly distribute the crispy fried onions on top.

Bake: Bake uncovered for 25–30 minutes, or until the casserole is hot and bubbly and the onions are golden brown.

Serve: Let cool slightly before serving. Enjoy warm and creamy!