Preheat a grill to medium-high heat (375 to 450 degrees Fahrenheit).
Bring the cod to room temperature for about 15 minutes.
Pat the cod dry with a clean towel. Rub it with the olive oil and sprinkle it with the kosher salt and fresh ground pepper. Then cover it with the homemade blackened seasoning or seafood seasoning on all sides.
Grill the cod over indirect heat for 4 minutes, until it releases from the grates. Flip and cook another 2 to 4 minutes, until the internal temperature is 130 degrees (right when the cod starts to flake when pulled with a fork). Allow to rest for a few minutes, then serve.