In a large stock pot, add shrimp shells and heads and saute over medium heat for 3 minutes, then add water.
If using shrimp paste, add shrimp paste and water together.
Add lemon grass stock chunks, ginger, garlic, chili peppers (more or less depending on your desired spice level), white onion, bay leaves, mushrooms, sugar, soy sauce, lime juice, sriracha, fish sauce, cilantro and salt.
Bring broth to a boil and simmer for 30 minutes, if your broth over reduces add a little more water.
Strain the broth with a fine mesh strainer.
Return broth to the pot and add shrimp, seafood of choice and mushrooms and cook for 3-4 minutes or until seafood is cooked thoroughly.
Serve with cilantro on top.
Enjoy!