Dice the Roma tomatoes into uniform 1/4-inch pieces and place them in a medium non-reactive mixing bowl.

Finely chop the white onion and cilantro, then add them to the bowl with the tomatoes.

Remove the seeds and membranes from the jalapeño, mince finely, and add to the mixture.

Pour the fresh lime juice over the ingredients and sprinkle with the kosher salt.

Toss all ingredients together with a spoon until evenly combined.

Let the mixture rest for at least 5 minutes at room temperature to allow the flavors to meld and the tomatoes to release their juices before serving.