Place large sauté pan over medium heat and add olive oil. Add mushrooms and cook 5-7 minutes, until softened. Set aside.
In a large bowl, mix together sesame seeds, vinegar, miso, sugar, ginger, and salt.
With a whisk, slowly incorporate sesame oil and olive oil into mixture.
Add slaw mix and mushrooms to bowl and mix thoroughly. Add additional sesame seeds if you prefer. Cover and refrigerate for 1 hour to marinate. Serve chilled.
Notes
*You can substitute soy sauce if white miso is hard to find where you live.