In a heatproof bowl, soak dried mushrooms in boiling water for 30 minutes, weighing down with a cup to ensure they remain submerged. Drain and discard liquid. Slice mushrooms thinly and set aside.
In a large saucepan or stockpot, heat oil over medium heat. Add garlic and ginger and cook, stirring, for 30 seconds. Add soaked dried mushrooms, fresh mushrooms, bell pepper, and finger chile to taste. Cook, stirring, until very fragrant, about 5 minutes. (Mushrooms shouldn’t be fully cooked at this point.)
Add stock, soy sauce and vinegar and stir well. Reduce heat, cover and simmer for until flavors are infused, about 10 minutes. Remove from heat and stir in sesame oil.
Ladle into warm serving bowls. Garnish with green onions. Serve immediately.
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