Cook noodles in a pot of boiling water until done. Drain.
In a large skillet, saute onion in oil. Add undiluted soup, chili powder, salt, and Worcestershire sauce. Simmer 5 minutes. Mix in noodles, 1 cup cheese, and tuna. Spoon into a greased 1 quart casserole dish.
Bake at 350 degrees F (175 degrees C) for 30 minutes. While still hot, sprinkle with remaining 1/4 cup cheese.