Remove seeds and membranes from the bell peppers and slice lengthwise into strips. Cut the beef across the grain into thin strips. Combine the soy sauce, garlic, paprika, ginger and two third of the oil. Add the beef strips, toss to blend and let the beef marinate at room temperature for at least 30 minutes. Prepare the vegetables while the meat is marinating. Remove the meat from the marinade. Strain the marinade and set aside. Heat the remaining oil in a wok or large, heavy frying pan. Add the beef and toss over high heat until the beef is well browned. If the meat isn't tender enough at this time, add a little water and simmer over medium heat for about 20 minutes. Remove the meat and set aside. Add all the vegetables except the tomatoes. Turn up the heat (medium or high) and toss the vegetables, cooking until tender-crisp (about 10 minutes). Add the meat. Mix the cornstarch with water and add to the pan. Cook, stirring steadily, until thickened. Add the tomatoes and salt and pepper to taste. Reheat. Serve over cooked rice or noodles.