Chicken Cauliflower casserole

This recipe was a free sample at a local super market. I made a few changes to it(obviously). I hope you'll enjoy.
Alfredo sauce,homemade is best
2 heads of cauliflower
1 store bought rotisserie chicken
1 bag of spinach(16 oz.)
a handful of Parmesan cheese
half a cup of bread crumbs
5 tbsp. butter
Prep work:
Steam cauliflower until tender
Take the meat off the chicken
Make Alfredo sauce
Cooking work:
Mix spinach,cauliflower,cheese,and chicken. Then add Alfredo sauce and mix.USE A LARGE POT OR BOWL.
Add to a large casserole dish and cook at 400 degrees for thirty minutes.
Halfway through the cooking process mix bread crumbs and butter and pour over top of casserole