Cook the pasta according to the package directions.
While the pasta boils, cook the onion and garlic in a large skillet over medium heat until the onion is soft. Add a bit of water if it begins to stick.
Add the asparagus and mushrooms to the skillet and cook until tender-crisp.
Stir together the miso paste, sesame oil, maple syrup and sriracha.
Drain the pasta and then combine pasta, vegetables and miso sauce.
Toss everything to coat it all in the sauce.
Serve topped with sesame seeds, if desired.
Notes
Miso is found in the refrigerated section, but you might not find it at every grocery. You can skip it, but it does add nice flavor to many recipes and will keep for a year or more in your fridge.