Heat oil in a large saucepot or Dutch oven over medium heat.

Add mushrooms, garlic, ginger and soy sauce and toss to coat.

Cook, stirring once or twice, until mushrooms are browned on edges, about 5 minutes.

Bruise stalk of lemongrass with the back of a knife to release oils and cut it into 3 pieces.

Add lemongrass to pot.

Pour in vegetable broth and increase heat to medium high, scraping bottom of pan to release any browned bits.

Stir in green onions, carrots, red peppers and tofu.

Bring to a boil and reduce to a brisk simmer for 5 minutes.

When vegetables are tender, remove from heat.

Remove lemongrass from pot and discard.

Put miso paste in a small bowl and add a tablespoon or two of hot broth from the pot.

Stir to dissolve miso, then stir dissolved miso into pot.

Ladle soup into bowls and garnish with cilantro or parsley.