Take the cream cheese from the refrigerator at least one hour before beginning the preparation, or microwave it for 30 to 60 seconds (it should be very soft).
Bring water to a boil for the broccoli. Start preparing all the recipe’s ingredients while you wait for the water to boil (check they’re all ready before beginning the sauce). I suggest melting the butter in the microwave in a small dish and leaving it aside until required.
Preheat your oven to 375F and move the rack to the top third of the oven.
Once the water is boiling, add the broccoli and simmer for two to three minutes, then drain and transfer to a 9×13-inch casserole dish.
Add the cooked chicken to the casserole dish (just put it beside the broccoli for now).
Add the cream cheese, cream, onion powder, garlic powder, Dijon, Worcestershire sauce, and salt and pepper to a skillet or medium pot. Stir/whisk it often over medium heat until the cream cheese has completely melted into the sauce (this should take about 5 minutes). Important: the sauce should not get too thick (it should be similar to Alfredo sauce). If the sauce looks too thick, add a touch more cream. The sauce will thicken more in the oven.
Take the pan from the heat and mix in half the cheddar cheese (stir until smooth).
Pour the sauce over the chicken and broccoli, then toss and evenly distribute the mixture.
Top the casserole with the remaining cheddar, followed by the Parmesan.
Add the panko breadcrumbs to the bowl that has the melted butter and stir until they’re evenly coated in butter.
Top the casserole with the breadcrumb mixture. Bake, uncovered, for 20 minutes. If you want the topping to be a little darker, broil it for a few minutes (watch it carefully).
Let the casserole sit for 5 minutes before serving.