Soak cedar plank in water for 1-2 hours.

In a small bowl combine soy sauce, brown sugar, vinegar, garlic, grated ginger, and red pepper flakes, and whisk until sugar is dissolved. Pour 1/2 of the marinade over the fish until well coated. Marinade in refrigerator for up to 2 hours.

Heat a small saucepan on medium-low heat and add the remaining marinade mixture. Whisk in the cornstarch until dissolved. Simmer sauce for 3-5 minutes or just until thickened.

Heat charcoal or gas grill on medium heat, Place soaked cedar plank on top of flames. Heat plank for 1-2 minutes then flip and heat another 1-2 minutes. Place salmon skin-side down on cedar plank. Season with salt and pepper. Grill over medium heat for about 12-15 minutes. Or until the salmon is just opaque in the center and flakes with a fork.

Brush some extra sauce on, add salt and pepper, and a squeeze of lemon if desired. Serve over rice.