Bring a large pot or dutch oven to medium-high heat. Once hot, add pork and season with salt & pepper. Then, add green onion, garlic and ginger. Allow the pork to cook until browned, using a spatula to crumble it into small pieces. Remove pork from the pot.
If there's excess pork grease still remaining in the pot, use that to sauté the mushrooms. If not, add a splash of olive oil. Then, add the sliced mushrooms and season with salt & pepper. Let them cook, undisturbed, for several minutes and then stir and cook for a few more minutes, until golden & tender.
Add back in the ground pork, shredded carrots and broth. Stir. Increase heat and bring the soup to a boil.
Once boiling, add the rice noodles and continue cooking until they are al-dente (check the package directions as each brand requires different cooking times).
Turn the heat off. Add in the tamari, rice vinegar and sriracha, if using. Stir.
Then, add the miso paste to your small sieve and lower it into the soup until it's slightly submerged. Push the miso through the sieve with the back of a spoon, allowing the hot broth to dissolve it. OR - add miso paste to a small bowl, add a bit of the hot broth and whisk until dissolve and smooth. Then, pour it back into the soup pot.
Taste the soup and adjust seasonings as needed.
Add in the Bok Choy, stir, and allow the residual heat to cook it for several minutes. Once the Bok Choy is tender and wilted, serve your soup with more green onion and sesame seeds. Enjoy!