To prepare the pesto, place all ingredients into a food processor fitted with the swivel blade and pulse until watercress is finely ground. The infused olive oil will be bright green. Keeps for a couple of weeks in the refrigerator.
To prepare sauce, heat olive oil and butter over medium heat in a large stockpot. Add zucchini, garlic and salt. Stir, coating the vegetables well. Sauté until vegetables begin to soften, 5 to 7 minutes. Cover and simmer 10 minutes. Zucchini will collapse and release its liquid, becoming “soupy.” Add water and wine, and continue cooking uncovered for another 7 minutes. Remove from heat and puree the mixture with an immersion blender. Taste for salt.
Cook pasta according to package directions. (Tagliardi, thin egg pasta squares, require 4 minutes cooking time.) Drain and return to pot.
Spoon warm sauce over pasta, and fold throughout—gently coating the pasta. Dot with watercress pesto oil. Dust with cheese, parmesan or pecorino.