Place a large skillet over medium-high heat and add in half of the oil. While oil heats, rub the bok choy with the miso paste using your fingers to cover completely. Once heated, add in the bok choy and cook 3 minutes per side or until charred. Remove the bok choy and set aside and then immediately add in the rest of sesame oil, white scallions, ginger, onion and garlic to the skillet and cook for 5 minutes or until onions soften. Then, pour in the stock and soy sauce, cover and bring to the boil. Then, add in the mushrooms, lower to a simmer and let cook for 5 minutes or until mushrooms soften. Then, add the zucchini noodles and cook for 2-3 more minutes or until noodles are cooked to al dente or your preference.Using pasta tongs, carefully transfer the noodles to two serving bowls and top with the bok choy. Then, ladle over with the broth mixture. Garnish with green scallions, sesame seeds and hot sauce, optional and serve immediately.