In a large pot, combine the pasta, tomatoes, leeks, zucchini, bell pepper, garlic, olive oil, lemon juice and zest, oregano, salt, red pepper flakes and basil. Add the water and stir. Bring to a boil, cover, and boil for 8 minutes. Give it a stir around the 5 minute mark to make sure nothing is sticking to the bottom of the pan and put the the cover back on. At 8 minutes, test the pasta for doneness. Remove the pot from the heat, stir, and let it sit for about 2 minutes to allow the sauce to thicken.Make the Vegan Hemp Seed Topping: In a food processor, combine the hemp seeds, nutritional yeast, sunflower seeds and salt and pulse to combine.Serve with the chopped parsley, toasted pine nuts and parmesan cheese or Vegan Hemp Seed Topping, if using.