-
Here's what I do:
Bring a large pot of boiling water to the boil, and dunk the whole octopus (beak removed) in it three times (use tongs!) and hold it under for about two seconds each time. This will acclimate the meat to the temperature so it won't seize up too much.
Then put it in the pot and boil it for about one hour, covered. After the one hour is up, remove the pot from the heat, and let the octopus remain the water, covered, for an hour. Remove the octopus from the water and cut into pieces, as desired (I like to leave my tentacle pieces fairly long). Then I marinate them in sea salt, red wine vinegar, parsley (or Greek oregano if you can get it) and garlic. Leave it to marinate for about an hour, maybe two. Finally, I grill it on a grooved cast iron pan. -
My favorite is marinated-- equal parts oil and lemon juice, w/ S&P, w/ parsley. A friend of mine makes this w/ a slight bit of soy sauce; I prefer it w/o. You can also include thinly-sliced shaved fennel if you want, but the octopus alone is good. Leave it in the marinade for a few hours.
-
-
I realize that you probably can't grill it, but lots of good tips here:
http://www.chowhound.com/topics/498812
I particularly enjoyed Caroline1's description of how to tenderize an octopus.

