1. The flavorings. Melt the lard or other fat in a medium-size skillet set over medium heat. For a milder dish, seed the chiles then chop them finely and add to the skillet, along with the onion and tomato. Cook, stirring frequently, until the onion has softened but is not brown, about 5 minutes. Reduce the heat to medium-low.
2. The eggs. Beat the eggs with the salt, just enough to combine the whites and yolks. Add them to the skillet and scramble until they are as sone as you like. Taste for salt, then scoop them into a warm dish and serve right away.