In a heavy skillet or stew pot, sauté the onions in moderately hot oil until golden. Stir in the tomatoes and green pepper. After a minute, add the spinach, salt and hot pepper. Cover, reduce the heat and simmer for 5 minutes. Thin the peanut butter with several tablespoons of warm water to make a smooth paste. Add to the pot. Continue cooking for another 10 - 15 minutes, stirring frequently. Add small amounts of water as necessary so that the stew does not stick to the bottom of the pot. Serve with rice.