Submerge the plank in water, placing a weight on top of it. Soak for 1 to 4 hours.
Prepare the buttermilk marinade. Add the buttermilk to a large mixing bowl or directly into a ziplock bag. Add the sliced or crushed ginger, the minced garlic, green onions, sliced lemon and the red pepper flakes.
Cut the fillet into individual salmon steaks. This allows for quicker, more even cooking, as well as the seasonings and marinade to cover more surface area. Add salmon to marinade in a ziplock bag (for easy clean up) for a couple of hours or up to overnight.
Preheat grill on high for 10 minutes. Preheat plank for another 3-4 minutes. Lower the temperature to Medium and cover. While your grill is heating, remove salmon from marinade and pat dry with paper towels. Season the salmon with S&P. Slather in your favorite teriyaki sauce. Add the ground ginger to the brown sugar and then apply an ample coating of brown sugar to the top.
Place seasoned salmon on preheated plank and allow to cook for 12-15 minutes, depending on the size and thickness of your steaks. Feel free to baste with additional teriyaki sauce. It should reach an internal temperature of 145 degrees, and should flake easily when a fork is inserted into the center of the thickest part.
Top with sesame seeds and thinly sliced green scallions, alongside some steamed broccoli and white rice or just a fresh salad. Enjoy!