Fill a stockpot with water and aromatics (carrot, celery, salt, peppercorns, half a lemon and laurel).
Bring water to a boil.
Before completely poaching the octopus let the tentacles touch the boiling water, moving the octopus up and down 3 or 4 times. This will nicely curl the tentacles for a prettier plate.
Cook the octopus until tender (according to its weight) in the covered stockpot over low heat. I cooked two octopus of 1 lb. each in 25 minutes, but a bigger one may well need 45 to 60 minutes. Try it with a fork after 25 minutes; if soft, remove and immediately place it in a bowl filled with ice and water. This will stop its cooking and it will prevent the octopus from becoming rubbery.
Heat a cast iron grill pan on the stove.
On a wooden cutting board, chop the octopus in 1-inch pieces (including the head that you or your trusted fish guy have previously cleaned).
When the grill pan is hot, grill the octopus until nicely charred. I like both the taste and the smell of lightly charred octopus!