You can buy the cedar planks at any hardware store, and Kaffir lime leaves are available at most Asian grocery stores or online.
1. Make Marinade: Combine mango juice, salt, chipotle powder, pepper, garlic and scallions in a bowl. Place fish in a 9x13-inch glass dish and cover with marinade. Marinate 1 to 2 hours in refrigerator.
2. Make Green Curry Sauce: Add 1 1/2 cans of coconut milk, Kaffir leaves, cinnamon, allspice and garlic to a saucepan. Roughly crush star anise by hand and add to pan. Bring to a low simmer for 10 to 15 minutes. Strain and discard solids, then return sauce to pan.
3. Place remaining coconut milk and all remaining ingredients except limes in a blender and process until smooth. Add to sauce in saucepan and cook for 1 minute. Remove from heat and cover. (If making ahead, cover the surface of the curry with plastic wrap while storing in the fridge. This will prevent oxidation).
4. Soak and drain cedar planks. Pat dry with paper towels and brush lightly with canola oil. Set a 5-gallon bucket of water near grill.
5. Preheat grill on high for 15 minutes. Place cedar plank in center of grill and grill for 2 minutes.
6. Prepare Fish: Reduce heat to low and place fish on plank, then immediately cover grill. Grill for approximately 4 to 5 minutes depending on heat of the fire and filet thickness. Whitefish should be slightly soft in the middle, not raw but medium rare, and seared on the outside. If plank starts to smolder or catch on fire, simply remove fish with spatula and drop plank into the 5-gallon bucket filled with water. Continue to grill fish until filet is cooked through. Season fish with salt and pepper
7. When fish is done, arrange on a platter or plates topped with green curry. Serve with lime wedges and additional cilantro. This dish is also good served cold.