Cook the tagliatelle in boiling water while preparing the cold parsley sauce.
In a blender, combine 1 bunch of parsley, tahini, walnuts, garlic, olive oil, and a little water to blend smoothly. The result should be a homogeneous mixture, not too runny or too dry.
Prepare the avocado by cutting it into small pieces.
Serve the cooked tagliatelle, add the sauce, and garnish with avocado.