Start by heating up olive oil in a large skillet over medium heat. Add the boneless skinless chicken breast, seasoning it with salt and pepper. Cook until golden brown and cooked through, ensuring not to overcook to avoid drying it out.
In the same pan, melt the butter. Once melted, add the flour and whisk until it is smooth and has a nice golden color. Gradually mix in the chicken broth and half and half, stirring continuously to avoid lumps. Monitor the sauce to prevent it from thickening too much.
Stir in the minced garlic, Dijon mustard, hot sauce, soy sauce, onion powder, oregano, parsley, paprika, and garlic salt. Allow the mixture to smell fragrant and savory, tasting as you go to achieve the right flavor balance.
In a pot, cook the fusilli pasta in salted water until al dente. Add the broccoli florets during the last 2 minutes of cooking. Drain the pasta and broccoli, ensuring they look vibrant and tender. Be cautious to not overcook the pasta, as it can turn mushy in the bake.
In a large bowl, gently mix the cooked chicken, fusilli pasta, broccoli, and sauce until everything is evenly coated. Take your time with this step for an even distribution of sauce.
Transfer the combined mixture into a greased casserole dish. Evenly sprinkle cheddar cheese and grated Parmesan over the top, ensuring all parts are covered for consistent cooking.
Preheat your oven and bake the casserole until bubbly and the top is golden. Pay attention to avoid burning the edges; this should take approximately 30 minutes.
Once the baking is complete, sprinkle crispy fried onions on top for extra crunch. This textural contrast should enhance the dish. Add them after baking to maintain their crunchiness.