Pre-heat oven to 350°
Put potatoes and onion in pot of water, bring to a boil for 5 minutes. Drain and set aside.
In a saucepan, melt margarine over low heat. Beat in flour with a wisk, continue to beat over medium flame until mixture is smooth and bubbly. Whip in boiling water, salt, soy sauce, garlic powder, and tumeric. Beat well to dissolve the flour mixture. The sauce should cook untill it thickens and bubbles. Whip in oil and nutritional yeast.
In a casserole dish put a layer of potatoes/onions. Spread cheese sauce on potatoes/onions. Add another layer, add more cheese, repeat 'till you are out of potatoes/onions and cheese. Cover and bake for 10 minutes. Uncover and bake for 5 more minutes.