Heat the cooking oil in a large pot over medium heat.
Add minced garlic, grated ginger, and chopped onion; sauté until fragrant and translucent, about 3-4 minutes.
Stir in ground turmeric and chili flakes (if using), cooking for 1 minute more.
Add diced bell peppers and julienned carrot; cook for 3-5 minutes until slightly softened.
Pour in fish stock/broth and bring to a gentle simmer.
Stir in coconut milk, lime juice, and lime zest; simmer for 5 minutes.
Add the fish pieces, simmer gently for 5-7 minutes until fish is cooked through and flakes easily.
Stir in fresh spinach or kale and cook until wilted, about 1-2 minutes.
Season soup with salt and pepper to taste.
Serve hot, garnished with chopped cilantro.