Saute onions in butter.
Cook noodles according to directions.
Melt Velveeta and Rotel in microwave until smooth. Add cheese/Rotel mixture to cooked noodles along with broth, chicken and onions. Mix well.
Place in a greased 9x12 oblong glass casserole dish. Bake at 350 degrees for 20 minutes.
Let stand 15-20 minutes before serving.