Gather the ingredients. Preheat the oven to 350 F and butter a shallow 2-quart casserole.
Cook the macaroni 2 to 3 minutes less than the package directions; drain and set aside.
Steam the frozen broccoli until just tender; drain, chop into bite-sized pieces, and set aside.
In a medium saucepan, melt the butter or margarine over low heat.
Add the flour, chopped green onion, salt, dry mustard, and pepper; stir until well blended.
Gradually stir in the milk until blended. Bring to a gentle boil; cook, stirring constantly, until the mixture is thickened and bubbly, about 2 minutes.
Stir in the cooked and drained macaroni, cooked broccoli, cubed ham, and shredded cheese. Transfer the mixture to the prepared casserole.
In a small bowl, combine the breadcrumbs with the melted butter; sprinkle over the casserole.
Bake for 30 minutes, or until golden brown.
Serve hot and enjoy.
