Step 1

Cook Chicken: Cut chicken into 1/2-inch pieces (Note 4), and cook them in large pan over medium heat until cooked through. Use slotted spoon to transfer only chicken to 8x8 inch baking dish (Note 5), leaving behind any liquid in pan.

Step 2

Make Sauce: Stir together all creamy mustard sauce ingredients in small saucepan over medium heat. Once it starts to simmer, turn off heat. Evenly pour sauce over chicken in baking dish, using spatula to scrape down saucepan to get every last bit of sauce.

Step 3

Assemble Casserole: Preheat oven to 375 F. Cut ham into 1/2-inch strips, patting dry with paper towels if wet, and add to baking dish. Then add green peas and swiss cheese on top. Stir everything directly in baking dish until well-mixed. Evenly top with cheddar cheese, then top with parmesan cheese.

Step 4

Bake: Bake uncovered at 375 F until casserole is heated through and starting to brown on top, about 30 minutes. Cool for at least 10 minutes, then cut into 4 equal portions and serve (Note 6).