In a medium saucepan, heat margarine. Saute onion and garlic until onion is softened. Stir in flour and paprika until well blended; cook for 1 minute. Stir in reserved liquid from tomatoes. Cook, stirring constantly, until sauce is slightly thickened, about 2 minutes. Add tomatoes and pepper; quarter tomatoes with kitchen shears. Stir until blended and heated through.