Get water boiling for noodles; heat pan for tomatoes and onions. Add the oil to the pan and once it's hot add the red pepper flakes. Once the oil is shimmering put in the onions, and turn the heat down to medium low. Pierce the tomatoes with your fingers while letting the juice and seeds stay in the can. Dice up the tomatoes after cutting off the hard flower part and add them to the pan once the onions are tender. Boil the noodles till al dente. Once the onions are clear add the tomatoes' juice and the salt. Let simmer until 1/2 the water has evaporated and the tomato onion mixture is thick. Drain the noodles; put them back the pot; throw in the tomato onion mixture.