Vegetarian Tom Yum Soup (Hot and Sour Soup)

Since the beginning of fall, as the weather becomes colder, it is difficult to have salads as part of our diet.  The solution I thought of was to have more of soups, different varieties of it. One more reason for this fondness for soups in this season is that starting with Diwali, there are a lot many holidays and festivals till the end of the year and it is a time when we all indulge on heavy, calorie rich foods. So it makes sense to have soups for lunch to compensate for that as well.
Tom Yum soup is popular in Thailand and neighboring countries. It is a clear soup, which is spicy and sour and so perfect for the cold weather.

Recipe Source:About.com
Ingredients:
1 t. vegetable oil
1 T. minced fresh garlic
2 t. fresh minced ginger (or sliced galangal)
3-4 thai chilies, seeded and finely diced (optional)
6 cups vegetable stock
2 stalks lemongrass, peeled and chopped into 4-inch pieces
2-3 whole kaffir lime leaves
1-2 t.(Thai roasted chili paset read the label to make sure that all ingredients are vegetarian), plus more for garnishing
2 tablespoons oil of nam prik pao(chilli paste)
1 t. sugar
2 T. soy sauce
2 T. fresh lime juice
1 cup fresh shitake or oyster mushrooms, sliced (if these aren't available, substitute crimini or button mushrooms)
1 cup chopped fresh tomato
1 lb. extra-firm tofu, drained and pressed, then chopped in 1" cubes
Fresh cilantro, for garnishing
Cooked noodles or rice, for serving
Method:

In a large stock pot, heat the vegetable oil over medium-high heat. Add the minced garlic, minced ginger, and thai chilies (if using). Cook for 2-3 minutes, stirring often, or until the garlic smells fragrant. Add the stock, lemongrass stalks, and kaffir lime leaves. Bring the mixture to a boil, then turn down the heat, cover the pot, and simmer for 5-10 minutes.
 Using a slotted spoon, remove the lemongrass stalks and kaffir lime leaves. Add the hot chili paste along with the chilli paste oil, sugar, soy sauce and fresh lime juice, stirring to combine, and bring the mixture back to a boil. Add the mushrooms  and cook for 2-3 minutes, or until the mushrooms have just slightly wilted. Turn down the heat to a simmer, then add the fresh tomato and extra firm tofu. Simmer for about 3-5 minutes more. Add salt or other spices as desired and serve hot with your favorite cooked noodles or rice. Garnish with fresh cilantro leaves and an extra few drops of chili paste if desired.