Add everything to a food processor and pulse until everything's broken down and well combined, it should still have a bit of texture and not be a sauce.

Start boiling your pasta. Sauté the onion, garlic and mushrooms with a pinch of salt for a couple of minutes over low/medium heat. After they are done add the coconut milk and boil the sauce. Now in a separate bowl mix the cornstarch and miso with water until everything's dissolved. Once the coconut/mushroom sauce comes to a boil add the cornstarch and miso mixture and stir until the sauce becomes creamy. Turn the heat back to low and add the cooked pasta, pesto and nutritional yeast and stir until everything's well combined. If you want you can mix 100 grams of baked onions through the pasta (this is completely optional)