01 - Bring a large pot of generously salted water to a rolling boil. Add the pasta and cook according to package directions until al dente. Before draining, reserve 1/2 cup of the starchy pasta water. Drain the pasta through a colander and set aside.
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 a vibrant green color is achieved.
03 - Taste the sauce and season with salt, pepper, and chili flakes as desired. If the sauce is too thick, add a few tablespoons of the reserved pasta water and blend again until it reaches a creamy, pourable consistency.
04 - Transfer the drained pasta to a large mixing bowl. Pour the green goddess sauce over the hot pasta and toss thoroughly until every strand or piece is evenly coated. Add additional pasta water a splash at a time if needed for a silky, glossy finish.
05 - Plate immediately while warm. Garnish with extra fresh herbs and an additional sprinkle of Parmesan if desired. Pair with a crisp Sauvignon Blanc or Pinot Grigio for a complete meal.