Generously grease 2 (1 pound) coffee cans, or 3 (1 lb.) vegetable or fruit cans, or two vegetable juice cans (pineapple or V8 work well); set aside. (The cans should only have one end removed.).
In a large bowl, combine the flour, baking soda and salt. Add raisins and walnuts, if desired. Toss to evenly coat the raisins and nuts with the flour mixture.
In a medium bowl, combine the oil, water, egg, vanilla, sugar, and molasses. Mix well.
Stir the wet mixture into the flour mixture only until dry ingredients are moistened.
Turn into prepared cans, filling evenly. Cover cans tightly with 2 layers of foil; secure with string or rubber band.
Cook with one of the two following methods:.
#1: Place a rack in a large kettle or pot. Place the cans on rack. Place kettle/pot over low heat. Add boiling water until halfway up cans. Cover; bring water to a gentle boil. Steam bread 2 1/2 to 3 hours or until a wooden pick inserted in center comes out clean. Add more boiling water during steaming, if necessary.
#2: Place a rack in a large kettle or pot. Place cans on the rack. Add boiling water to the kettle/pot and cover with a lid. Place the kettle in a 325° oven and steam for 2 hours and 45 minutes, replacing boiling water as needed.
Carefully remove bread from cans. Cool on racks at least 30 minutes before slicing.