Watch Alton Brown on TV Food Network at 11pm tonite. It's a repeat of him doing "Chimney" tuna. He uses a "chimney" charcoal starter to lightly sear a tuna loin. I tried this for Christmas Eve this past year and it came out excellent.
I tried it last summer and it is really good. It sears the outside fast before cooking the tuna too much. I started using it for burgers if I make just 1 or 2. I have a gas grill also, but you just can't beat the taste of real charcoal.