Take the cream cheese out of the fridge at least an hour prior to starting the recipe or microwave it for 20-30 seconds (it should be very soft).
Boil a pot of water for the broccoli. While you're waiting for it to boil, start prepping all the recipe ingredients (ensure they're ready to go before starting the sauce). For the melted butter, I recommend microwaving it in a small bowl and setting it aside until needed.
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 cook it for 2-3 minutes, then drain well and add it to a 9x13 casserole dish.
Add the cooked chicken to the casserole dish (just put it beside the broccoli for now).
To a skillet or medium saucepan, add the cream cheese, cream, onion powder, garlic powder, Dijon, Worcestershire sauce, and some salt & pepper. Cook it over medium-high heat, stirring/whisking nearly constantly until the cream cheese has melted into the sauce (this should take about 5 minutes). Important: Don't let the sauce get too thick (it should be similar to Alfredo sauce). If the sauce seems a bit too thick, add in another splash of cream. The sauce will thicken more in the oven.
Take the skillet off the heat and stir in half of the cheddar cheese (stir until smooth).
Pour the sauce over the chicken and broccoli, then toss and spread it in an even layer.
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 prior to serving.