Cook macaroni according to package directions; drain. In a skillet over 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 in a greased three quart casserole dish. Combine bread crumbs with remaining butter; sprinkle over top. Bake uncovered,at 350 degrees for 23 to 30 minutes, until golden.