Rinse the cleaned octopus under cold running water and pat dry.

In a large stockpot, combine 8 cups of water with a halved onion, smashed garlic cloves, bay leaves, whole peppercorns, vinegar (or wine), and a generous pinch of salt. Stir to combine.

Bring to a gentle boil, then reduce to a low simmer. Dip the octopus into the liquid three times, then lower fully into the pot.

Cover loosely and let simmer for 45 to 60 minutes, checking for doneness.

Turn off the heat and let the octopus rest in the poaching liquid for 10 minutes. Slice into bite-sized pieces, drizzle with olive oil and lemon juice.