Place cedar planks on hot grill until they are smoking. Flip over, brush with miso glaze, then place filets on planks. Close lid and cook for 2-3 minutes. GENTLY flip filets over then brush more miso glaze over them. Move to cooler side, and continue to cook until internal temperature reaches 145 degrees, occasionally brushing with more miso glaze. Remove from grill, using a spatula remove from planks, and serve.