1. Rub fish all over with lemon juice and sprinkle with 1/2 teaspoon salt. Set aside for 30 minutes.
2. Meanwhile, place the rest of the ingredients except oil in a blender and blend until smooth.
3. Heat 2 tablespoons oil in a pan, pour ground paste. Cook for a few minutes on medium heat until moisture evaporates and sauce thickens. You may notice oil separating at this point. Cool sauce down.
4. Smear the sauce all over fish and refrigerate for at least 3-4 hours.
5. Heat 2 tablespoons oil in a non-stick frying pan. Fry fish on medium heat for 2-3 minutes on each side until crispy. Serve hot with Thai sweet chili sauce.