Fry the onion with garlic and a bit of salt until they turn translucent but aren't caramelized. (It doesn't need the sweetness of caramelization since the coconut milk is sweet.) Remove from the heat, stir in spices and tomato paste. Return to heat and fry until everything blends and the tomato paste looks a bit darker.
Add the coconut milk and bring to a simmer.
Add the bell peppers, jalapeno pepper, green onions, and fish. Return to a simmer. Cover and simmer for 5 minutes, or until the fish flakes.
Remove from heat. Stir in lime juice and fish sauce. Taste and adjust seasoning.
Excellent with rice.