01 - In a mixing bowl, whisk together olive oil, smoked paprika, cumin, chili powder, garlic powder, onion powder, salt, black pepper, and lime juice. Add the chicken thighs or flank steak, turning to coat evenly. Let marinate for at least 15 minutes at room temperature.
02 - While the protein marinates, combine the finely chopped tomatoes, red onion, minced jalapeño, cilantro, and lime juice in a bowl. Season with salt and pepper to taste. Stir well and set aside to allow the flavors to meld.
03 - Light the charcoal and allow the coals to develop a white-gray ash coating. Spread the coals evenly and bring the grill to medium-high heat, approximately 400°F to 450°F.
04 - Place the marinated protein directly over the hot coals. Grill chicken thighs for 4 to 5 minutes per side until the internal temperature reaches 165°F and char marks appear. For flank steak, grill 2 to 3 minutes per side for medium-rare doneness. Transfer to a cutting board and rest for 5 minutes before slicing thinly against the grain.
05 - While the protein rests, lay tortillas directly over the grill grates. Toast each side for 15 to 30 seconds until lightly charred and pliable. Stack and wrap in foil to keep warm.
06 - Layer sliced grilled protein onto each warm tortilla. Top with shredded lettuce, diced tomatoes, red onion, cilantro, and avocado slices. Spoon fresh salsa over the top and add crumbled queso fresco or shredded cheese if desired. Serve immediately with lime wedges on the side.