Preheat oven to 400°. In a bowl, combine Thai peppers, lemongrass, garlic, cilantro, lime juice, coconut cream, maple syrup, and white pepper. Squeeze grated ginger into the bowl to extract juice; discard ginger solids.

Place banana leaves or parchment papers on a large, rimmed baking sheet. Spoon a little of the lemongrass sauce in the center of each leaf or sheet of paper. Place fish on top, then spoon remaining sauce over fish. Fold top and bottom sides over fish, overlapping; fold in remaining sides, forming a square packet around each fillet. Using a strip of foil, crimp top two edges together to keep each packet from unfolding. Slip a thin strip of banana leaf (or a piece of kitchen string) under and around each packet and tie in a bow or square knot.

Bake 25-30 minutes, depending on thickness. Remove from oven. Transfer packets to serving plates and carefully remove foil seals, leaving string intact (as decoration). Serve hot.