To Make Thai Red Curry Paste:
Whirl all ingredients in a food processor or blender, scraping down sides as needed, until puréed, 1 to 2 min. Use immediately or refrigerate in a jar for up to a month.
To Make Spicy Thai Fish:
Heat a large frying pan over medium-high. Add 1 tbsp vegetable oil. Sprinkle 2 firm fish fillets (such as tilapia) with 1/8 tsp salt. Add fish to hot pan. Cook until a knife inserted into the thickest part of fish and held for 10 sec comes out warm, 3 to 5 min per side. Transfer to plates. Reduce heat to medium. Add 1 tsp vegetable oil, 1/2 cup finely chopped red pepper, 2 tbsp Thai red curry paste and 1 to 2 tbsp coconut milk. Cook until pepper is soft, 2 to 3 min. Spoon sauce over fish.