Rinse the octopus and rub with coarse salt. Arrange a layer of thick sliced tomato on the bottom of the saucepan. Place the octopus on top and cook covered for approximately 25 minutes. It is necessary to test frequently the tenderness of the octopus. If the octopus is not fully cooked or if it is overcooked it will have a hard rubbery consistency.
Remove the octopus from the saucepan and rub it with a kitchen cloth to get rid of some of the dark skin. Rinse immediately. Cut the head off and discard or reserve it for another preparation. Cut the tentacles in pieces.
Place octopus on a serving dish and add lemon juice, blended aji, onion, salt and pepper.
Mix well and marinate for 15 to 20 minutes before serving.
Garnish with sweet potato slices and cooked kernels.