Prepare the Tom Yam Stock: Boil prawn shells and heads in water with salt and red chilies for 30 minutes. Sieve the liquid.

Prepare the Chili Paste: Blend dried shrimp, vegetable oil, chili powder, onion, garlic, tamarind juice, sugar, salt, and shrimp paste.

Boil tom yam stock in a pot over medium-high heat.

Add green chilies, lemongrass, galangal, kaffir lime leaves, small onions, and coriander root to the stock.

Bring to a boil and cook for 10 minutes to infuse flavors.

Add cubed chicken breast pieces and cook for an additional 10 minutes until cooked through.

Add halved button mushrooms and chopped shiitake mushrooms.

Cook for 5 minutes, then add quartered tomatoes and cook for 2 more minutes.

Incorporate chili paste and cook for 2 minutes.

Add lime juice, fish sauce, and prawns to the soup.

Cook for 2 minutes, or until the prawns are pink and cooked.

Remove from heat.

Stir in chopped coriander and Thai parsley leaf.

Garnish with sliced red chili.

Serve immediately.