Soak cedar plank in warm water for at least 30 minutes, overnight if possible.
Preheat grill to medium heat (~400 degrees F) charcoal or gas grill.
Remove plank from water and place steelhead fillet skin-side down on top. Pat the surface of the flesh with a paper towel to remove excess moisture then brush olive oil.
In a small dish combine the cracked pepper, Old Bay seasoning and the dried dill then sprinkle over the fillet,
Place cedar plank directly on grill, close the cover and cook for 15-18 minutes.
Transfer the plank from the grill and place on a work space, tent with foil and allow to rest for 5 minutes.
While the trout is resting, melt the butter in a small microwaveable dish and stir in the chopped fresh dill, set aside.
To serve, cut the fillet into 4 equal portions and serve each portion with a drizzle of the dill butter. Add lemon wedges and fresh dill sprigs to garnish.
Notes
Alternative to using the grill, you can place the plank directly on the oven rack and bake for 13-15 minutes at 400°F until it registers 145°F on an instant-read thermometer.