Peel and slice potatoes. Line cookie sheet with tin foil. Spray foil with non-stick spray (Pam) In large bowl, combine potatoes, green onions, green peppers and white onions. Pour onto foil lined pan. In same bowl, mix barbecue sauce, water, and dry spices. Pour over top of potatoes. Bake in 200ºC oven for 45 minutes. Turn and seperate to ensure even cooking. Bake an additional 10 minutes or so. (Baking time depends on how thick you slice the spuds) Sprinkle grated cheese on top of cooked potatoes, and continue cooking until cheese has melted and the edges become crispy. Let sit for about 4-5 minutes before serving to allow the cheese to set up a bit.