Ready a stainless steel bowl.
Wash the tomatoes and the chiles. Let dry on a clean kitchen towel.
Wash the cilantro in a large bowl containing at least 1 quart of very cold water. Handle it somewhere between vigorously and gingerly in the water, separating and agitating all the while. Drain in a colander. Repeat the process. Spin in a salad spinner for optimal effect (after both washings).
Cut the lime for juicing. Set aside.
Using a small serrated knife, cut the tomatoes into 1/4-inch slabs. Then cross-cut them into a proper dice with your chef's knife.
Cut the tops off the chiles, split them lengthwise, and then quarter them lengthwise. You're quartering them so you have relatively flat surfaces to work with. Now, julienne and finely dice them. Nice work!
Dice the onions. Brag about your increasing knife skills confidence. Now, look at your fingers. Still there!
Chiffonade the cilantro.
Combine all of your knife work in the stainless steel bowl.
Squeeze the lime over the mixture. You want about 1 tablespoon of juice.
Put the salt in your hand and sprinkle over the salsa with a sense of fanfare and exuberance. It doesn't matter if no one is watching. You know what you did!
Let the mixture sit at room temperature for anywhere from 15 minutes (good) to 1 hour (glorious) before serving.
Note: This salsa is best served the day you make it. Beyond that, it'll taste a little less vibrant and the texture won't be the same.