Place a large dutch oven or pot over medium heat. Add sesame oil and swirl to coat. Add in the onion and cook for 3-4 minutes until translucent. Add in ginger and garlic, stirring until fragrant.
Pour in water, tamari, rice vinegar, miso paste mixture, chili garlic sauce, maple syrup, salt and pepper, and bring to a boil. Reduce heat to medium low and simmer for 10 minutes.
Meanwhile, cook noodles to al dente according to package instructions in a separate pot. Drain and set aside.
After 10 minutes of simmering, add the mushrooms and optional dried chilis to the broth. Simmer gently for an additional 5 minutes until mushrooms are tender. Gently stir in tofu cubes.
To serve, place noodles in large serving bowls and ladle the soup over the noodles. Top with fresh green onions.