Bring a large pot of salted water to a boil (about 4 quarts water and 2 tablespoons salt). Add zucchini and boil for 6-8 minutes or until tender. Use tongs or a fine mesh sieve to transfer the zucchini to a high-speed blender to steam off a bit (don’t throw the water away!).
Add the pasta to the boiling water and cook according to the package instructions, adding your greens in with 1-2 minutes left. Drain and set aside.
In the blender, add the soaked or boiled seeds, water, oil, lemon, garlic, fennel, oregano, salt, and red pepper flakes (if using) and blend on high until smooth (this should take about 1 minute).
Transfer the pasta back to the pot and pour the sauce over top (scrape it all out!). Toss to coat. Taste and add more salt, if needed.
Serve topped with black pepper, plenty of cheese (if using), and toasted seeds (if using).