Start by heating the oil in a heavy pan and put in the tumeric and some salt. Fry for a few seconds and then add the cubed potatoes, turning frequently so that they turn yellow from the tumeric. Cook them for 5-10 minutes (they will complete their cooking later) and remove them from the oil and set aside. Adding more oil if necessary, saute the onion slices until they are soft and transparent. Add bay leaf, cumin, ginger and chili powder. Stir well; add tomatoes. Cook until they begin to break down, and then add the cabbage bit by bit, stirring it in well so that it is sauteed in the spices. Cover and cook gently for 3-5 minutes. Finally put in the peas and semi-fried potatoes and seasoning. Mix well, replace the cover and continue to cook for 5-10 minutes or until potatoes are tender.