1) Put the olive oil and onion in a large skillet over a medium heat and cook until the onion has softened and turned a rich golden color.
2) Stir in the garlic, cook for 1 minute.
3) Pour 4 quarts of water into a large saucepan or pot and place over a high heat.
4) Uncover the skillet and add the zucchini and bell peppers. Season with salt and add red pepper flakes. Cook, stirring frequently, until the vegetables start to become tender: about 5 minutes.
5) When the water for pasta is boiling, add 1 tablespoon of salt and drop in the pasta all at once, stirring well.
6) Meanwhile, add the tomatoes to the sauce and continue cooking until they have reduced and separated from oil: about 5 minutes. Remove the skillet from the heat and set aside.
7) When the pasta is cooked al dente, drain it and toss it thoroughly with the sauce. Taste it for salt and serve at once.