Heat vegetable oil in a pot over medium heat. Add the chopped onions and saute until slightly golden. Increase heat to medium-high. Add the chicken and saute until no longer pink, stirring occasionally. Add the turmeric powder and stir gently. Add water, curry powder, cumin ground and salt. Cover the pot and bring to boil. Reduce heat to medium-low and simmer for 30 minutes, stirring occasionally. Add more water during cooking, if necessary.
Then add white sauce and mushrooms, cover the pot and cook until chicken and mushrooms are tender and stew is thickened. Serve with rice.