Mix coconut milk, red curry paste (start with 1 teaspoon and add more depending on how spicy you like it), soy sauce and palm sugar.
Cut off root end and stalk of lemongrass, leaving about 3″ of the “plumper” part. Remove any loose outer leaves. Pound lemongrass with back of knife to release flavor, then cut into 1″ pieces.
Open banana leaf and spread ginger and lemon grass in center of leaf. Lay fish on top. Spread coconut curry sauce on top. Fold banana leaf over fish, enclosing ends with a wooden skewer or toothpick.
Steam fish for 15-20 minutes, depending on thickness of fish.
Serve with steamed brown rice and stir-fry leafy green vegetables. Open packet at the table for extra sensory effect.