One 3-inch piece ginger, peeled and roughly chopped
¼ cup soy sauce
¼ cup white distilled vinegar
2 tablespoons freshly ground black pepper
1 tablespoon tamarind pulp
1 teaspoon sugar
1 teaspoon kosher salt
1½ pounds flank steak
½ red onion, plus more for serving, thinly sliced
2 tablespoons freshly squeezed lime juice
Grilled naan, for serving
Lime wedges, for serving
Cilantro leaves, for garnish
Directions
Make the masala: In a 12-inch skillet, heat the canola oil over medium-high heat. Add the onions and cook until translucent and lightly golden, 3 to 4 minutes. Add the curry leaves, garlic, serrano and ginger, and cook until fragrant, 2 minutes more. Remove from the heat and transfer to a blender with the remaining masala ingredients. Blend until smooth, then let cool completely.
Make the tacos: In a large bowl, toss the flank steak with the masala to coat. Refrigerate for at least 1 hour. Meanwhile, in a small bowl, toss the sliced red onion with lime juice and set aside.
Light a grill or heat a cast-iron grill pan over high heat. Grill the steak, flipping once, until caramelized and medium rare, 7 to 8 minutes. Let rest for 5 minutes, then thinly slice against the grain on a bias.
Serve the steak with pieces of grilled naan, sliced red onion and lime wedges, garnishing with cilantro leaves.