Bring a large of pot of water to a boil. Lightly salt and then add the pasta and cook until just tender, about 8 minutes. While the pasta cooks, set a large skillet over medium heat and add the oil. Add the onion and garlic and cook, stirring, 2 to 3 minutes. Add the zucchini and cook 2 minutes more. Add the tomatoes and cook 3 to 4 minutes, or until softened. Stir in the basil, salt and pepper. When the pasta is cooked, reserve 1/2 cup of its cooking liquid, and then drain the pasta well. Add the pasta and reserved cooking liquid to the skillet and toss to combine. Serve, tableside, with freshly grated parmesan cheese.
Note: For added colour, use 1 green and 1 yellow zucchini, when the latter is available.