In a bowl, whisk together vinegar, soy sauce, garlic, lime juice, and olive oil.
Add salt, pepper, garlic powder, chili powder, oregano, cumin, and paprika.
Place the flank steak in a dish and pour the marinade over it. Turn to coat well, cover, and refrigerate for at least 6 hours or overnight.
In a small bowl, combine chopped onion, cilantro, and lime juice. Mix well and refrigerate until ready to serve.
Toast the dried chile pods in a skillet for 1–2 minutes until fragrant, then soak them in hot water for 30 minutes.
Preheat oven to 450°F.
Place tomatoes, onion, jalapeños, and garlic on a baking sheet and roast for about 20 minutes until slightly charred.
Blend the roasted vegetables with the softened chiles until smooth. Season with salt and pepper to taste.
Heat a grill pan or skillet over medium-high heat with a light drizzle of oil.
Remove steak from marinade and cook whole for about 4–5 minutes per side for medium-rare.
Let the steak rest for 5 minutes, then slice thinly against the grain.
Warm the corn tortillas in a skillet until soft and pliable.
Assemble tacos with sliced carne asada, onion relish, and homemade salsa. Add cheese and a squeeze of lime if desired.
