Read through all the directions before starting to ensure everything is ready at the same time.
Start the water for the pasta and bring to a boil.
While the water for the pasta is coming to a boil, sauté the mushrooms over medium heat in a dry non-stick skillet until cooked down, about 10 minutes. If you don't have a non-stick skillet, you may need 1 teaspoon of oil so they don't stick. Set aside.
The pasta water should be boiling now. If so, cook your pasta according to package directions for al dente. Drain and set aside when done.
While the pasta is cooking, sauté the onions in ¼ cup vegetable broth in a large skillet until soft and translucent, about 4 to 5 minutes. Add the garlic and sauté another 1 minute.
Add the other ¼ cup vegetable broth and simmer until absorbed, about 5 minutes.
In a small bowl, whisk together the tahini, non-dairy milk, apple cider vinegar, lemon juice, nutritional yeast, salt and maple syrup, if using, until smooth. The sauce will taste pretty strong right out of the gates, but once tossed with the pasta and mushrooms, it will mellow.
Pour the tahini sauce into the skillet with the onions and garlic. Whisk it to warm through just for a minute and take off the heat.
Add the pasta and the mushrooms to the sauce immediately and stir to combine. Add additional non dairy milk or water 1 tablespoon at a time to thin, if necessary.
Throw in the chopped fresh parsley and walnuts, stir, and serve immediately.