Boil water and cook your noodles according to package instructions — but stop cooking and drain just before they are fully cooked. MAKE SURE TO SAVE AT LEAST A CUP OF PASTA WATER.
In a food processor, combine all the ingredients for the pesto except the olive oil. Put on the lid, but remove the insert, and slowly stream in olive oil while you pulse the mixture until you get the desired consistency, like a thick sauce.
In a saucepan over medium heat, add the olive oil and onion and cook until soft and fragrant, about 3-4 minutes. Add the asparagus and cook another 2 minutes. Add the mushrooms and cook another 2 minutes.
Lower heat to low. Add in the drained pasta and pesto and stir to combine. Splash in a little pasta water until you get a creamy consistency you like.
I like to serve with more fresh grated Parmesan on the side, and more fresh herbs!