Trim the darker colored ends of lemongrass stalk, leaving the lighter colored ends, about 3 or 4 inches. Using the back of your knife, pound each stalk to loosen. Slice each stalk in half lengthwise. Use as is or tie lemongrass together with food grade string.

Heat oil in a large pot over medium-high heat. Add lemongrass stalks and sauté, until fragrant, about 3 minutes. Add onion and sauté for about 5 minutes. Add garlic and ginger, and sauté until fragrant, about 1 minute.

Add vegetable broth, chili, and lime leaves. Cover with a lid and bring to a boil. Reduce heat to medium low, simmer to let the flavors infuse, 20 minutes.

Remove lemongrass stalks from soup. Add grape tomatoes, red bell pepper, Bok choy, and mushrooms. Simmer uncovered until the mushrooms have softened, about 5 minutes. Add lime juice, tamari, sugar, and coconut milk and stir and let heat to serve. Garnish with cilantro leaves and/or chopped scallions.