Prepare the shrimp, squid, mushrooms, tomatoes, lemongrass, and cilantro.
In a pot, bring chicken stock, lemongrass, and lime leaves to a boil.
Add minced garlic, ginger, chili peppers, and Tom Yum paste; simmer.
Add the prepared seafood, mushrooms, and tomatoes, and cook until done.
Season with fish sauce, lime juice, and sugar.
Top with cilantro and chili peppers to finish.