Ingredients

1 tablespoon canola oil
4 cooked boneless, skinless chicken breasts, cut into bite-sized pieces
6 tablespoons salted butter, divided
(1 tablespoon, 2 1/2 tablespoons, 2 1/2 tablespoons)
2 cups small-cubed ham
1 1/4 cups grated Swiss cheese
1 1/4 cups grated Monterey Jack cheese
1/2 cup panko breadcrumbs
1/4 cup all-purpose flour
2 cups milk
1 cup chicken broth
2 tablespoons Dijon mustard
1/2 teaspoon cayenne
Kosher salt and freshly ground black pepper

Prep
Grease a 9-by-13-inch baking dish with 1 tablespoon butter.
Preheat the oven to 350 degrees F.
Chicken
Cut chicken into bite-sized pieces. Season with salt and pepper.
Heat canola in large non-stick pan on medium-high (3/4 of the way between low and high)
Fry chicken, stirring often, until cooked through, about 8-10 minutes. Use slotted spoon to move chicken to a bowl.
Ham
Cut ham into small cubes (about 1/4 inch)
Put the ham on a paper towel-lined plate and microwave for 3 minutes to reduce the moisture content.
Cheese
Mix together the Swiss and Monterey Jack cheese in a 4-cup measuring cup.
Panko
Melt 2 1/2 tablespoon of butter in the microwave.
Put panko in a 1-cup glass measuring cup
Pour melted butter on panko and use a fork to mix well.
Sauce
Melt the remaining 2 1/2 tablespoons butter in a large steel skillet over medium heat.
Add the flour to skillet and cook for 2 to 3 minutes, whisking constantly.
Whisk in the milk, broth, Dijon and cayenne and let it cook until it begins to thicken, whisking often, about 10 minutes.
Remove from the heat and stir in 1 cup of the cheese until melted. Season with salt and pepper.
Assembly
Put about a third of chicken in a layer in the bottom of the prepared baking dish.
Top with half the ham.
Sprinkle over 1/4 cup of the mixed cheese.
Repeat 1 more time: (third of the chicken, then other half of the ham, 1/4 cup of the cheese)
Then finish with a layer of chicken.
Pour the sauce over the casserole.
Sprinkle over the remaining 1 cup cheese
Then spread the panko mix on top
Bake until the top is browned and the casserole is bubbling, 25 to 30 minutes.