01 - Whisk together olive oil, lime juice, garlic, cumin, paprika, chili powder, oregano, salt, and pepper in a medium bowl until thoroughly combined.
02 - Add chicken thighs to the bowl, tossing well to coat evenly with the marinade. Let sit for at least 15 minutes, or up to 2 hours for deeper flavor penetration.
03 - Heat a large skillet or grill pan over medium-high heat. Cook chicken thighs for 5-6 minutes per side until cooked through and nicely browned with a slight char.
04 - Transfer cooked chicken to a cutting board and allow to rest for 3 minutes. Chop into bite-sized pieces, about ½-inch cubes.
05 - Heat corn tortillas in a dry skillet or directly over a gas flame for approximately 30 seconds per side until soft, pliable, and lightly charred.
06 - Fill each warm tortilla with chopped chicken, then top with diced onion, fresh cilantro, avocado slices, and crumbled cotija cheese if desired.
07 - Serve immediately with fresh lime wedges and salsa or hot sauce on the side for squeezing and drizzling.