In a medium serving bowl, mix together the finely chopped onion, jalapeño, lime juice, and salt. Let this mixture rest for around 5 minutes, allowing the flavors to meld while you prepare the tomatoes and cilantro.
Add the chopped tomatoes and fresh cilantro to the bowl. Stir everything together until the ingredients are well combined. Taste the mixture and adjust the salt as needed to enhance the flavor.
For optimal taste, allow the pico de gallo to marinate for at least 15 minutes, or refrigerate it for several hours to deepen the flavors. When serving, use a slotted spoon or a large fork to avoid transferring excess tomato juice.
Store any leftovers in an airtight container in the refrigerator for up to 4 days, keeping the vibrant freshness intact. Enjoy as a dip or as a zesty accompaniment to your favorite dishes.