Slice the thick ends off each lemongrass stalk. Use the back of your knife to pound each stalk lightly, to help release the oils. Slice each stalk into 3-4" strips.
Heat a large pot over medium-high heat. Once hot, add oil and lemongrass stalks. Cook for 2 minutes, stirring regularly. Once lemongrass is fragrant, add diced onion. Sauté for 3 minutes, or until onion begins to soften. Then add garlic and galangal, cooking for 2 minutes until fragrant.
Add vegetable stock, Thai red chili peppers, and Kaffir lime leaves. Bring to a boil. Once boiling, reduce heat to medium-low and cover with a lid. Simmer for 15 minutes. Then, use a slotted spoon to remove lemongrass from the pot and discard. While the soup boils, use a spiralizer to turn your zucchini into “noodles”.
Once the lemongrass is removed, add tomatoes and mushrooms to the soup. Simmer, uncovered, for approximately 5 minutes, or until the vegetables are soft. Season with ¼ cup lime juice, tamari, coconut sugar and coconut milk. Stir to mix well.
To serve, transfer zucchini noodles into bowls. Ladle soup on top. Garnish with cilantro, green onions, and/or lime wedges.