Cook the pasta al dente according to the package instructions (this should take about 6 to 9 minutes, depending on the brand and kind of pasta you’re using), then reserve some of the pasta water, drain, and set aside.
While the pasta is cooking, sauté the onions, garlic, and mushrooms in the oil in a nonstick pan or pot over medium heat for 5 minutes.
Lower the heat to low, then mix in the salt, pepper, and spinach and mix until the spinach has reduced in volume (about 1 minute), before adding the tahini, lemon juice, nutritional yeast, and pasta water.
Once everything is well incorporated, cook for 2 more minutes, then add the pasta, mix, and serve.
Enjoy!