We slice skirt steak and cook it quickly at a high temperature to save time and keep the meat tender. Make sure you save the super flavorful collected juices from the steak and onions to drizzle on your tacos.
Cut the steak along the grain into 3-inch pieces, then slice each piece across the grain into ⅓-inch-thick strips. Toss the steak in a medium bowl with the chili powder, oregano, sugar, ¾ teaspoon salt and a few grinds of pepper.
Heat a large nonstick skillet over high heat. Meanwhile, wrap the tortillas in a clean dishtowel, and microwave at 100 percent for 1 minute. Let sit, wrapped in the dishtowel, until ready to serve.
When the skillet is hot, add the oil. Add the seasoned steak in an even layer. Don’t stir for 2 minutes, then give the steak a good stir and let cook until browned, about 1 ½ minutes more. Transfer the steak to a medium bowl. Immediately add the onions to the skillet, and stir until brown and slightly softened, about 1 1/2 minutes; transfer to the bowl with the steak, and stir to combine.
Set up a taco bar with the steak and onions, wrapped tortillas, sour cream, guacamole, salsa verde, pico de gallo and cheese.