Prepare grill by lighting 4 quarts of charcoal (1 starter chimney's worth), or turning gas grill to medium-high.
Examine steaks for pin bones by rubbing fingers over surface of meat. If found, remove with bone tweezers or pliers reserved for culinary uses.
Using a sharp paring or boning knife, trim bones from the cavity side of the steak. Trim the stomach flaps so that 1 side is missing about 2 inches of skin and the other, 1 inch of meat. Roll the skinless section up into the hollow of the cavity, then wrap the other around the outside to form a round resembling a filet mignon. Tie in place with 2 passes of butcher's twine. (Do not tie it too tight or fish will pop out during cooking.)
Combine cumin, coriander, fennel, and peppercorns on a double-thick piece of aluminum foil and toast over grill, shaking gently until seeds become fragrant. Crush seeds in a coffee/spice grinder. Coat steaks lightly with oil, season with salt, then liberally season both sides of steaks with the toasted spices.
Quickly wipe hot grill grate with a rag or towel dipped in a little oil, then grill fish to medium rare, about 3 minutes per side. (Fish should be well colored on the outside and barely translucent at the center.)
Serve steaks alongside simple salad dressed with Veni, Vedi, Vinaigrette.