Start by thoroughly cleaning the octopus under cold running water, ensuring any residue is removed.

In a large stockpot, combine the cleaned octopus with sliced onion, halved lemons, smashed garlic cloves, bay leaves, peppercorns, and a sprinkle of salt. Add enough water to cover the ingredients and bring to a gentle simmer.

Cook for 45 to 60 minutes, or until the octopus is fork-tender. Let it cool in the cooking liquid.

While the octopus simmers, whisk together olive oil and either red wine vinegar or lemon juice in a bowl, then add parsley, oregano, salt, pepper, red pepper flakes, and lemon zest.

Once the octopus has cooled, cut it into pieces suitable for grilling and combine with half of the prepared vinaigrette.

Preheat your grill to medium-high heat, and clean and oil the grates.

Thread octopus pieces onto skewers if desired, brush lightly with olive oil, and grill for 2 to 4 minutes per side.

Once grilled, let the octopus rest for about 5 minutes, drizzle with the reserved vinaigrette, and serve with lemon wedges.