Core the tomatoes and finely chop them into small even pieces. Measure the onion amount shown in the card and chop it finer than the tomato.
Combine the chopped tomatoes and onion in a glass, ceramic, or stainless-steel bowl.
Squeeze in the juice of 1 lime and stir. Taste; add the second lime if the mixture still tastes flat or dry.
Add a few shakes of natural sea salt. Stir and wait briefly for the salt to draw juice from the tomatoes before adjusting.
Finely mince 2 tablespoons cilantro and fold it in until evenly distributed. Keep the tomato and onion pieces distinct rather than crushing them.
Cover and refrigerate for at least 2 hours so the lime, salt, onion, cilantro, and tomato juices meld. Stir before serving.