Season fish with salt and pepper. Heat oil in a large skillet and add fish. Lightly brown fish on one side. Flip fish over and cook for 1 minute. Add onion, garlic, fish sauce and soy sauce. Cook for 2 to 3 minutes more. Add coconut milk and ginger. Remove fish when just cooked and keep warm. Stir in curry paste, lime juice, brown sugar and green onion. Heat to a boil. Taste the sauce. If you want it hotter, add a little more curry paste.