Begin slicing onion and garlic. Put sesame oil in medium sized soup pot and heat at medium-low. Add onion when oil begins to simmer. After translucent, add garlic.
Add sliced shiitake mushrooms. Add small amount of salt to help them sweat.
After mushrooms begin to soften, add carrot and bell pepper. Saute until all vegetables are soft. Add a bit more oil, and then add tofu. Saute until slightly golden. Add a dash of rice vinegar/black vinegar and soy sauce to deglaze pot and loosen vegetables and tofu.
Add 8 cups water. Add approximately 2 teaspoons of chicken base. Add approximately 2 tablespoons of spicy chili sauce.
Bring to boil and add udon noodles and chopped cabbage. Boil as directed ( approximately 8 minutes). Reduce to simmer and then season to your taste. Remember that soy sauce will make it salty, so go slow. Add the spice as hot as you like. Top with chopped green onions.