Bring a large pot of water to a boil, adding a tablespoon of sea salt. Submerge the cleaned octopus into the boiling water, ensuring it's fully covered.
Reduce the heat to maintain a gentle simmer and cook the octopus for about 45 minutes to 1 hour, or until it becomes tender when pierced with a knife. The water should emit a gentle bubbling sound.
Remove the octopus from the water and let it cool slightly on a plate or cutting board. Pat it dry with paper towels to remove excess moisture, which will help get a good char on the grill.
Brush the octopus tentacles generously with olive oil on all sides to enhance browning and prevent sticking on the grill.
Preheat your grill to high heat until hot and slightly smoky. Place the octopus tentacles directly on the grill grates.
Grill the octopus for about 3-4 minutes per side, turning with tongs, until the tentacles develop a bubbly, crispy char and smell smoky and fragrant.
Once grilled, transfer the octopus to a serving platter. Squeeze fresh lemon juice over the tentacles and season with black pepper to taste.
Let the octopus rest for a minute before slicing into pieces. The final dish should have a crispy exterior with a tender, juicy interior, ready to be enjoyed with additional lemon slices if desired.
