Preheat the oven to 350℉/177℃. Lightly spray a 9×13-inch baking pan with nonstick cooking spray.
Put your broccoli florets into a pan with just enough water to cover them. Heat the water to a boil and cook with the lid on for 5 minutes. When the broccoli is tender, drain and set aside.
Next, season chopped chicken with salt and Creole seasoning (salt-free). Thoroughly mix.
Heat oil in a large skillet, add the chicken, and cook it for about 5–6 minutes or until cooked through. Set aside.
Add butter to the skillet, and let it melt. Follow with the minced garlic and onions. Cook until onions wilted—3-4 minutes.
Stir in the flour and cook it for about a minute to get rid of the raw flour taste.
Slowly add milk and chicken stock because you don't want the mixture to form any lumps. Simmer for about 5 minutes or until it thickens slightly. Add Creole seasoning, and continue cooking for about 2 more minutes.
Stir in the cheeses and Worcestershire sauce, and stir until the cheese melts and everything is evenly combined and smooth. Sprinkle with salt, pepper, and a pinch of nutmeg to taste.
Mix the Panko breadcrumbs and melted butter in a small bowl until the butter is absorbed and your mixture is crumbly.
Add cooked broccoli to the prepared baking or casserole dish. Then add the chicken and follow with the sauce.
Top with the breadcrumb mixture.
Bake in the preheated oven for 18-20 minutes or until bubbly and lightly brown.