The chile. Roast the poblano over an open flame or close up under a hot broiler, turning it until the skin is evenly blackened. Cool until handleable, then rub off the blackened skin, tear it open and pull out the stem and seed pod, then quickly rinse to remove any stray seeds of bits of skin. Cut into ¼-inch pieces. If using chipotle chiles, set the slices aside to add later.
Cook the chorizo and onion. In a large (10-inch) non-stick skillet, cook the chorizo over medium heat for a couple of minutes, breaking up the clumps, until it begins to render its fat. If little comes, add a little vegetable oil, so that fat or oil covers most of the skillet. Add the onion and cook, stirring regularly, until the onion is softened and beginning to brown and the chorizo is cooked through, about 8 minutes longer.
The eggs. While the onion is cooking, crack the eggs into a medium-size bowl and beat just until the yolk and white are thoroughly mixed—it shouldn’t still be streaky nor should it be beaten long enough to become foamy. Season with a generous ½ teaspoon salt.
The scramble. Because I like to scramble eggs slow and low, I turn the heat down almost to medium-low at this point. When the onion and chorizo are about ready, stir in the chile (poblano or chipotle) and cook for a minute or 2. Add the eggs to the pan, then start the gentle scramble, using a silicone spatula to slowly and deliberately scrape up the cooked eggs from the sides, moving it toward the center and letting the uncooked egg run into the open spaces. When the eggs are barely set (they will still moist looking), remove the pan from the heat, gently stir a couple more times, letting the heat of the pan finish the cooking, and you’re ready to serve with a sprinkling of cilantro, delicious salsa and warm tortillas.