The holy Thai trio of lemongrass, garlic, and ginger in a garden version of Tom Yum Soup is a powerfully delicious soup that is quick and easy to put together.
Trim 1-inch off both ends of lemongrass stalk, and discard. Use the back of your knife to pound each stalk. Cut each stalk into about 3-inch lengths, then cut each piece in half lengthwise.
Heat oil in a large pot over medium-high heat. Add lemongrass 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 from soup. Add grape tomatoes, Bok choy, and mushrooms. Simmer uncovered until the mushrooms have softened, about 5 minutes. Add lime juice, tamari, sugar, and coconut milk. Stir to mix well.