Melt the margarine in a pot, add flour and stir until smooth. Gradually add milk and the chicken stock. Let it boil. Add the seasonings and then the sliced mushrooms. Let it cook. Take a greased 9 x 13 inch baking dish, spread a layer of cooked rice then cover with a layer of the chicken mixture. Pour the white sauce on top and sprinkle vegetables over it. Spread thickly with grated cheese and sprinkle the black olives all....