Step 1

Preheat oven to 375 degrees F. Put a large pot of water on to boil. Cook broccoli in the boiling water until just tender and bright green, about 3 minutes. Transfer to a large bowl with a slotted spoon. Add pasta to the boiling water and cook according to package directions. Drain and rinse with cold water. Transfer to the bowl with the broccoli.

Step 2

Heat butter in a large skillet over medium heat. Add chicken, onion, salt and pepper. Cook, stirring frequently, until the onion has softened and the chicken is no longer pink throughout, 6 to 8 minutes. Add flour and mustard. Stir until coated. Add milk and bring to a boil. Cook, stirring, until thickened slightly, 2 to 4 minutes. Transfer to the bowl with the broccoli and pasta. Stir in cheese, ham and parsley. Transfer the mixture to a 9-by-13-inch baking dish, spreading evenly. Combine panko and oil in a small bowl. Sprinkle over the casserole.

Step 3

Bake until the casserole is heated throughout and the breadcrumbs are beginning to brown, about 30 minutes (or 50 minutes, if casserole has been frozen).