Thaw the octopus overnight in the refrigerator or submerge in cold water for a couple of hours.

In a large pot, combine octopus, lemon slices, and red wine vinegar. Add enough water to cover the octopus partially.

Bring to a boil over medium-high heat, then reduce to a low simmer and cook for 40-50 minutes.

Carefully remove the octopus and let it cool for about 10 minutes.

Using a knife, separate the tentacles from the head and slice tentacles into 3-4 inch pieces.

Preheat your grill to medium-high heat. Brush the grill with olive oil and pat the octopus dry.

Grill the octopus pieces for 10-12 minutes, turning every 2-3 minutes.

Transfer the grilled octopus to a serving plate and drizzle with olive oil and lemon juice, then sprinkle with oregano.