01 - In a mixing bowl, combine 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.
02 - Light the charcoal and allow coals to heat until covered with gray ash, indicating medium-high heat. Spread coals in an even layer for direct grilling.
03 - Place the marinated meat directly over the hot coals. Grill chicken thighs for 4 to 5 minutes per side, or flank steak for 2 to 3 minutes per side, until nicely charred and cooked through. Transfer to a cutting board and rest for 5 minutes before slicing thinly against the grain.
04 - While the meat rests, place tortillas directly over the grill for 15 to 30 seconds per side until lightly charred and pliable. Stack and wrap in foil to keep warm.
05 - In a bowl, combine chopped tomatoes, red onion, jalapeño, cilantro, and lime juice. Season with salt and pepper to taste. Stir gently and set aside.
06 - Layer sliced meat over warm tortillas. Top with shredded lettuce, diced tomatoes, red onion, cilantro, and avocado slices. Spoon fresh salsa over each taco and add crumbled queso fresco if desired. Serve immediately with lime wedges.