In a large pot, heat the oil over medium heat. Once hot, add lemongrass stalks, ginger, green onion, and chilis. Fry for about 5 minutes.
Next, add the chopped tomatoes and pineapple, and cook for 5 more minutes, or until the tomatoes have released their juice.
Pour the 4 cups of water into the pot. Add the corn, coconut sugar, salt, and soy sauce. Let simmer for about 20 minutes. If using, dilute the tamarind paste in a couple of tablespoons of warm water and let it sit for 5 minutes. Strain and add to the broth.
In the meantime, cook the noodles, wash and prepare the vegetables, and dice the tofu and/or vegan chicken.
Place the pot on a portable burner on the table and let it simmer. Place the vegetables, noodles, and tofu around it, and enjoy! Each guest can cook the veggies of their choice for a few minutes in the pot. Fill your bowl with noodles, top with tofu, veggies, and pour hot broth over them.