Cook macaroni according to package directions; drain.
Meanwhile, in a skillet over medium-low heat, cook onions in one tablespoon melted butter for one minute. Stir in flour until smooth.
Gradually stir in milk and broth, cooking and stirring until slightly thickened. Stir in chicken, seasonings, cheese, peas and bacon. Mix in macaroni.
Spoon into a greased 3-quart casserole dish. Combine bread crumbs with remaining butter; sprinkle over top.
Bake, uncovered, at 350 degrees for 25 to 30 minutes, until golden.