In a large pot of boiling water, cook pho rice noodles until "al dente". The should be almost completely cooked, but still have a bit of a bite to them so that they are perfectly cooked once you add to the broth. Drain and rinse under cold water. Separate into servings otherwise it will all stick together as one clump. Add spinach, beans sprouts, and chopped green onion on top of the servings and set aside.
In a large pot, cook mushrooms in olive oil, white parts of green onion, chili flakes, and soy sauce until mushrooms have browned. Pour in vegetable broth and bring to a boil. Taste and adjust salt/add granulated mushroom broth.
Pour broth over noodles in their respective serving bowls. Add sriracha and hoisin sauce to taste and serve immediately.