Halve and core the Roma Tomato, then finely dice the flesh into roughly 1/4-inch pieces; if you prefer a less watery salsa, scoop out the seeds before dicing.
Peel and finely dice the White Onion into pieces similar in size to the tomato so the texture is balanced.
Remove the stem from the Serrano Chile, slice it open, remove seeds if you want less heat, and finely mince; use gloves if you’re sensitive to capsaicin.
Roughly chop the Cilantro, including some of the tender stems, and add to a mixing bowl with the tomato, onion, and serrano.
Squeeze fresh Lime Juice over the mixture, start with about 1–2 tablespoons, and sprinkle in Sea Salt to taste—about 1/2 to 1 teaspoon to start.
Gently toss everything together until evenly combined, then taste and adjust lime and salt as needed; if too spicy, add a bit more tomato or a pinch more salt.
Let the pico rest for at least 10–15 minutes at room temperature to allow the flavors to meld, or refrigerate up to a few hours before serving for a cooler, slightly milder result.
Serve chilled or at room temperature with tortilla chips, on tacos, grilled fish, or as a bright condiment for any savory dish.
