Pat the fish dry, cut into chunks, and season lightly with a pinch of salt and pepper.
Warm the olive oil in a heavy pot over medium heat.
Soften the onion and bell pepper until translucent, about 5–6 minutes.
Stir in the ginger and garlic; cook until fragrant, about 1 minute.
Toast the tomato paste, stirring, for 1 minute to deepen the flavor.
Pour in crushed tomatoes and stock, then whisk in coconut milk, sugar, salt, pepper, red pepper flakes, and turmeric.
Bring to a gentle simmer and cook uncovered 10–12 minutes to meld flavors.
Slide in the fish and simmer gently until just flaky, 6–8 minutes.
Stir in lime juice, taste, and adjust seasoning. Ladle into bowls and top with cilantro and green onions.