Wash the beans & rice in plenty of cold water. Combine about 4 cups of water with beans & rice & cook for 5o minutes or until the beans are soft. Drain, reserving the stock for later. Heat oil in a skillet. Fry the onions for 3 minutes. Add the carrots & cookk covered for 5 minutes. Add the cooked beans & rice. Stir well & let saute for a few minutes, ensuring that the mixture does not burn. Combine the siy sauce, tomato paste, herbs & stock. Mix well & pour into the skillet. Bring to a boil, reduce heat to very low, partially cover & simmer gently for 30 minutes, stirring frquently to prevent it burning. Add more stock if necessary. Transfer into a casserole. Top the cooked vegetables with mashed Potatoes. Bake in a preheated oven at 180ºC for 40 minutes, or until the Potatoes are browned. Serve with vegetables or a green salad.