Sauté Aromatics
Heat the olive oil in a large pot over medium heat. Add the diced onion, garlic, and minced ginger, and sauté until softened and fragrant, about 3-4 minutes. Add the fresh chilies and cook for another minute.

Add Liquids and Seasoning
Pour in the fish stock or vegetable broth and coconut milk. Stir in the fish sauce, lemon juice, turmeric, chili powder (if using), and season with salt and pepper. Bring to a boil, then reduce the heat and let it simmer for 5-10 minutes to allow the flavors to meld.

Cook the Fish
Add the fish fillets to the soup and cook for 5-7 minutes, until the fish is cooked through and flakes easily with a fork.

Taste and Adjust
Taste the soup and adjust the seasoning, adding more lemon juice or salt if needed for balance.

Serve and Garnish
Ladle the soup into bowls and garnish with fresh cilantro or parsley, and optional lemon slices for extra flavor. Serve hot.