Mix the Spice Rub: Combine the smoked paprika, ground cumin, garlic powder, onion powder, dried oregano, cayenne pepper, kosher salt, and black pepper in a small mixing bowl. Stir with a spoon until all seven spices are fully incorporated into a uniform powder blend. This dry rub is applied before cooking and forms the seasoned crust on the chicken surface.
Season the Chicken: Pat the chicken thighs completely dry with paper towels on a cutting board, pressing firmly to remove surface moisture from both sides of each piece. Coat all four thighs evenly with the spice rub, pressing it firmly onto the flesh so it adheres. Set the seasoned thighs on a clean plate and rest them uncovered at room temperature for 15 minutes. This resting period allows the salt to draw out and reabsorb surface moisture, which strengthens the crust formation during searing.
Heat the Skillet: Heat 2 tablespoons of avocado oil in a 12-inch cast iron skillet over medium-high heat for 2 minutes until the oil shimmers and thin wisps of smoke appear at the edges of the pan.
Sear the Chicken Thighs: Place the seasoned chicken thighs smooth-side down in the hot skillet using tongs, spacing them at least 2.5cm / 1in apart to prevent steaming. Cook for 6 minutes without moving them until the underside develops a deep reddish-brown crust and lifts cleanly from the pan surface. Flip each thigh once and cook the second side for 5 minutes until the internal temperature reads 74°C / 165°F on an instant-read thermometer inserted into the thickest part of the meat.
Rest and Slice the Chicken: Transfer the cooked chicken thighs to a clean cutting board and rest them undisturbed for 5 minutes. Resting allows the internal juices to redistribute evenly throughout the meat before cutting. Slice each thigh against the grain into strips approximately 1cm / 0.4in wide using a sharp chef's knife, then drizzle the sliced chicken with 1 tablespoon of fresh lime juice and toss briefly to coat.
Warm the Tortillas: Place each corn tortilla directly over a gas burner set to medium heat for 30 seconds per side until the tortilla develops light char spots and turns pliable, or warm all 8 tortillas in a dry skillet over medium heat for 30 seconds per side until soft and heated through.
Assemble the Tacos: Lay two warm tortillas flat on each plate. Divide the sliced chicken evenly across all 8 tortillas, placing the strips in the center of each one. Top each taco with a portion of diced white onion, fresh cilantro, sliced avocado, and crumbled cotija cheese. Serve immediately with salsa roja and lime wedges on the side.
