Chop the onion, deseed and chop the green pepper, peel and grate the carrot and slice the mushrooms, halving them across the other way first if they are large.                 Saute the vegetables in the water or stock, in a large frying pan, until most of the liquid is gone and the vegetables are soft. Mix the remaining ingredients together in a bowl, adding a bit of water if you wish (makes a thinner sauce) and add to the vegetables in the pan. Mix well and cook, stirring, over low heat for about a minute until thickened. Pour over hot, split baked potatoes with a crisp green salad on the side.