Remove insides/viscera from head sac and wash octopus thoroughly under cold running water.
Bring large pot of water to a boil over high heat. Working with one octopus at a time, using a fork, pierce the head and dip, tentacles first, into the boiling water. Hold it in the water for about 5 seconds, then lift it out. Repeat the dipping two more times, and return to boiling water. Dipping the octopus 3 times is said to tenderize the octopus and it causes the tentacles to curve.
Partially cover the pot and adjust the heat to maintain a gentle simmer. Cook until the octopus are tender when pierced with a knife. If you aren’t sure, taste it. It should be tender, not chewy or rubbery. Once done, remove octopus and place on plate to cool down.
Remove the dark skin and suction cups on the tentacles with paper towels or scrape gently with knife. Cut the tentacles and head into pieces.
Put the sliced octopus in a bowl and add the olive oil, lemon juice, parsley, garlic, and salt. Stir well. Let marinate and refrigerate. Serve cold.
Tip: when preparing marinade, do so like you would a salad. If you need more oil, add it. If you need more lemon juice, add it. Enjoy.
Also, thaw frozen octopus in refrigerator. Always be safe.