Place the octopus in a pot and cover with cold water. Cook over medium flame until the water begins to boil, then reduce heat and simmer the octopus until tender. This will take between 1-2 hours. To check for tenderness, you should be able to pierce the thickest part of the tentacle easily with a paring knife.
Allow the octopus to cool in the water, then remove and pat dry with a paper towel. For maximum char, let the tentacles dry sitting on paper towel in the fridge for a further 2-3 hours. The drier they are, the more char you will get without overcooking them.
Light a grill for high heat cooking, 230 degrees or more.
Douse the tentacles in half of the olive oil, then sprinkle over half of the salt.
In a small bowl, combine the remaining olive oil, salt, oregano and black pepper. Add the juice of one of the lemons. Cut the remaining lemon into wedges and set aside.
Once your grill is hot, lay the tentacles directly over the coals to char and crisp on the edges. Leave them for 2-3 minutes, then flip them over and char the other side for a further 2-3 minutes. Remember – the octopus is already cooked, you are just applying the flavor of the grill, and so the grilling will be very quick. Basically, cook the octopus until you have the color you want then remove.
Drizzle with the lemon, oregano and oil mixture and serve with extra lemon wedges.