Cut cooked octopus into bite-size pieces and half cherry tomatoes. Add them to the bowl, mix, and let marinate for 30-45 minutes refrigerated. Chop the rest of fresh cilantro and add to the ceviche before serving. Taste ceviche and correct seasoning if needed. To serve, spread a layer of guacamole, top it with octopus ceviche, and enjoy with freshly grilled tostadas ot blue corn chips.