Prepare ingredients: halve and chop each lemongrass stalk into 3 pieces, slice the ginger into rounds, mince the garlic, trim and roughly chop the baby bok choy, and ensure the mushrooms are chopped. Measure out 1 tablespoon cornstarch and 1/2 tablespoon cornstarch separately; beat the 3 eggs in a small bowl and set aside.

Heat 1 tablespoon olive oil in a large saucepan or pot over medium-high heat. Add the 2 cinnamon sticks, 1 star anise, the prepared lemongrass, the sliced ginger, the minced garlic, and the optional ½ teaspoon red pepper flakes. Cook, stirring frequently, until the spices are very fragrant, about 3 minutes.

Add the 4 cups low-sodium chicken broth and 2 tablespoons liquid aminos to the pot and stir. Bring the mixture to a full boil, then reduce the heat to low, cover, and simmer for 15 to 20 minutes.

While the broth simmers, heat the remaining 1 tablespoon olive oil in a separate skillet over medium-high heat. Add the chopped mushrooms and the prepared baby bok choy and sauté until browned and softened, about 5 to 8 minutes. Transfer the cooked vegetables into the simmering broth.

Taste the broth and add more liquid aminos if desired. Use a slotted spoon to remove and discard the ginger rounds, cinnamon sticks, star anise, and lemongrass pieces.

Make the cornstarch slurry: stir 1 tablespoon cornstarch into a small bowl, add about 1/3 to 1/2 cup of the hot broth from the pot, and whisk until fully dissolved. Return the pot to a very gentle simmer and stir the slurry into the broth.

Add the remaining 1/2 tablespoon cornstarch to the beaten eggs and whisk until combined.

With the broth at a gentle simmer, slowly pour the egg-and-cornstarch mixture into the pot through the tines of a fork (or a small sieve), pouring a little at a time and whisking the broth gently between pours to create thin egg ribbons.

Keep the soup at low heat and whisk occasionally for a couple of minutes, until the egg is fully set and the soup has slightly thickened. Turn off the heat.

Ladle the soup into bowls, garnish with the chopped green onion, and serve.