• Fresh (this includes frozen), cleaned octopus.
  The Greek like to use frozen octopus as they say freezing tenderizes the cephalopod.
  I purchased a 3.1 kg frozen specimen.
   
• Oil.
  I use extra virgin olive oil.
   
• Grilled or roasted garlic.
   
• Condiments.

2. Method
 

• Wash the octopus.
   
• Cut the octopus into 8 segments, each with one tentacle (after cutting off the head).
   
• OPTIONAL (coil the tentacles):
  Blanch the ends of each tentacle by dipping it into boiling water.
  A nice permanent coil will develop.
   
• Place portions of octopus in a temperature stable plastic bag; remove most of the air and then seal the bag.
  The bag can be a vacuum bag or a zip-lock bag.
  I placed two portions in each plastic bag.
  
  At this preparation stage, some people load the octopus bags with oil, salt, herbs and spices.
  I chose not to, preferring to add these only before grilling.
   
• Place all the bags into a water bath and bring the bath temperature to 65^oC.
   
• Let the bags sit in the bath for at least 3 hours for a "bitey" tenderness (not overall soft); or 4 hours for a more tender result.
  I used a sous vide cooker (see http://clemkuek.com/photoalbum/photo_696_4m.html).
  You can replicate the effect of a sous vide cooker by just using hot water at the desired temperature in a container.
  Change the hot water regularly to maintain the temperature (monitor using a thermometer).
  The key is to maintain exposure of the octopus to a temperature below boiling for a long period of time (slow, low heat cooking).
   
• After your preferred cooking time, cut a small portion of the octopus and test for tenderness.
  If still not tender enough, continue to cook for a longer period.
   
• When cooking is done, you will notice that a lot of water has come out from the octopus.
  When estimating the quantity to cook for your dining requirements, assume that your octopus will shrink to half the starting size/weight.
   
• Drain off/surface dry the octopus.
   
• Add oil (I used extra virgin olive oil as per the Greeks), salt, pepper, herbs and other condiments to taste to a bowl and coat the octopus with the dressing.
   
• Char each tentacle portion on a hot grill until a nice colour has developed.
  Some charring is desirable as this will be tasty and visually attractive.
  Do not leave too long on the grill as this may dry out the octopus too much (remember that the octopus is already cooked by this stage).
  Your grilled octopus is now ready!
   
• Serve with lemon slices and your favourite sauces.