Marinate the steak
Pulse the garlic and jalapeño in a food processor until finely chopped. Add the cilantro and pulse a couple more times. Transfer to a baking dish or zip-top bag large enough to hold the steak. Add the oil, orange juice, lime juice, 1/2 tsp. salt, and a few grinds of pepper and stir to combine. Add the steak and marinate for at least 1 hour at room temperature or up to 3 hours in the refrigerator.
Pickle the onion
In a medium bowl, toss the onion with the salt and sugar to coat well. Let sit at room temperature until the onion softens, 15 to 20 minutes. Transfer to a fine-mesh strainer and rinse under cool water while tossing with your fingers to remove the salt and sugar. Pat dry on paper towels. In a small bowl, combine the onion and vinegar. Cover and refrigerate until needed.
Make the salsa verde
Put the tomatillos, cilantro stems, onion, jalapeño, and garlic in a 2-quart saucepan. Add 1-1/2 cups water and cook over medium heat until the onion is translucent and the tomatillos are tender, about 30 minutes. Using an immersion blender, regular blender, or food processor, purée until almost smooth. Allow the mixture to cool. Add the chopped cilantro leaves and lime juice and season to taste with salt. Refrigerate until needed. (Leftover salsa will keep for a week.)
Grill the steak and serve
Prepare a high (500°F to 600°F) charcoal or gas grill fire. Remove the steak from the marinade, season with salt and pepper, and grill, flipping once, until grill marks form on both sides and cooked to your liking, about 3 minutes per side for medium rare (135°F).Transfer to a cutting board and let rest for 5 minutes.
Meanwhile, warm the tortillas on the grill until light grill marks form on both sides and they soften, about 30 seconds. Slice the steaks with the grain into 4- to 5-inch-long pieces, then against the grain into thin slices no wider than 1/4 inch.
Assemble the tacos with the tortillas, steak, salsa, pickled onion, cilantro, and cheese. Serve with lime wedges for squeezing over.
nutrition information (per serving):
27, Fat Calories
240, Saturated Fat
42, Monounsaturated Fat
54, Polyunsaturated Fat
Photo: Scott Phillips