Ultimate Mock Mac and Cheese Casserole with Broccoli, Chicken, and Bacon

Nonstick cooking spray

large head cauliflower, chopped

chopped broccoli

cooked chicken, cubed

?4 cup heavy cream

cream cheese, sliced

1?2 teaspoons Dijon mustard

?2 teaspoon kosher salt

?4 teaspoon ground black pepper

?8 teaspoon garlic powder

shredded Cheddar cheese, divided

cooked bacon, chopped