Peel, clean, and wash the shrimp. Cut the shrimp and tuna into cubes and place them in a bowl. Add enough lime juice to cover the seafood, season with salt and pepper, cover the bowl with plastic wrap, and refrigerate for 1 hour.

Meanwhile, peel the cucumber, remove the seeds, and dice it into small cubes. Dice the tomatoes as well.

Finely chop the onion, cilantro, and chilies (if using).

After the seafood has marinated and the shrimp have turned pink, drain off the excess lime juice. Add all the chopped vegetables, pour in some tomato or vegetable juice (about 1 cup or to taste), and mix until everything is well combined. Adjust the seasoning, refrigerate for 15 minutes, and serve with avocado, tostadas, tortilla chips, and/or saltine crackers.