Cook noodles in a pot of boiling water until done. Drain.
In a large frypan, saute onion in oil. Add undiluted soup, chilli powder, salt and Worcestershire sauce. Simmer 5 minutes. Mix in noodles, 1 cup cheese and tuna. Spoon into a greased 1 litre casserole dish.
Bake at 180 degrees C for 30 minutes. While still hot, sprinkle with remaining 1/4 cup cheese.