In a large pot, pour in the 6 cups of low-sodium chicken broth and bring it to a simmer over medium heat. This will be the flavorful base of your Tom Yum Soup.
Add the prepared lemongrass, ginger, and minced garlic to the simmering broth. Allow these ingredients to steep for about 5-7 minutes, releasing their beautiful aromas.
Toss in the Thai chilies or jalapeño slices. Adjust the amount based on your heat preference. Let it simmer for an additional 3 minutes.
Stir in the sliced mushrooms and the wedges of tomato. Allow these to cook for about 5 minutes, so they become tender and flavorful.
Next, add the peeled and deveined shrimp to the pot. Cook for 3-5 minutes, or until the shrimp turn pink and opaque.
Incorporate the fish sauce, lime juice, low-sodium soy sauce, and sugar into the soup. Stir well to combine and let it simmer for another minute to meld the flavors.
Remove the pot from heat. Serve the soup hot, garnished with fresh cilantro leaves and optional lime wedges for an extra zing.