Trim each Brussel sprout and cut 1/8 inch deep x on the base of each one. Steam the sprouts in a a basket for 12 minutes, until tender. Drain. In a large skillet, heat ½ cup water over moderate heat. Cook the onion and the pepper until tender. Bring the remaining water to a boil, and pour it over the tomatoes into cold water. Let stand for 1 minute, then plunge the tomatoes into cold water. Add the Brussel sprouts, tomatoesin the skillet and heat through. Season with salt and pepper.