Preheat Your Oven: Preheat your oven to 350°F (175°C).
Mix the Base: In a large mixing bowl, combine the shredded chicken, steamed broccoli, cream of mushroom soup, and milk. Stir until well blended.
Add the Cheese: Fold in ¾ cup of the shredded cheddar cheese, reserving the rest for the topping. Season with salt and pepper to taste.
Transfer to Baking Dish: Pour the mixture into a greased 9x13 inch baking dish, spreading it evenly.
Top with Breadcrumbs and Cheese: Sprinkle the remaining shredded cheddar cheese over the top, followed by breadcrumbs if using.
Bake: Place in the preheated oven and bake for 25-30 minutes or until the cheese is bubbly and golden brown.
Serve and Enjoy: Let it cool slightly before serving. Enjoy your Cheesy Chicken and Broccoli Bake warm!