Prepare a stove-top griddle or outdoor grill with the rack set 1 inch above the coals. Allow the grill to get very hot.
Meanwhile, brush the butterfish with the olive oil and season with salt and pepper. Grill the butterfish about 3 minutes per side, until the fish just begins to flake. Arrange 2 butterfish on each of 4 dinner plates, garnish with the parsley, and serve.