01 - Bring a large pot of generously salted water to a rolling boil. Add the pasta and cook according to package instructions until al dente. Reserve ½ cup of starchy pasta water before draining in a colander.
02 - While the pasta cooks, place the basil, parsley, chives, tarragon (if using), avocado, Greek yogurt, olive oil, lemon juice, garlic, and Parmesan into a food processor or blender. Process on high until completely smooth and vibrant green.
03 - Taste the sauce and season with salt, pepper, and chili flakes as desired. If the sauce is too thick, blend in a few tablespoons of the reserved pasta water until you reach a creamy, pourable consistency.
04 - Transfer the drained pasta to a large mixing bowl. Pour the green goddess sauce over the top and toss thoroughly until every strand or piece is evenly coated. Add additional pasta water as needed for a silky, glossy finish.
05 - Plate immediately while warm. Garnish with extra fresh herbs and an additional sprinkle of Parmesan if desired.