Marinate the Chicken: Whisk together olive oil, lime juice, minced garlic, cumin, chili powder, smoked paprika, onion powder, salt, and pepper in a medium bowl. Add the chicken pieces into this marinade ensuring they are well-coated on all sides. Cover the bowl with plastic wrap and refrigerate it for at least 30 minutes; marinating longer will intensify the flavor.
Preheat the Pan: Heat a large skillet or cast-iron pan over medium-high heat until hot enough to sear meat effectively without sticking.
Cook the Chicken: Remove the marinated chicken from the bowl letting any excess marinade drip off before placing it directly into your hot pan. Cook each side of the chicken pieces for about 5-6 minutes until they reach an internal temperature of 165°F (74°C).
Rest and Slice the Chicken: Transfer your chicken onto a cutting board allowing it to rest for about five minutes; then slice the chicken into thin strips.
Warm the Tortillas: Warm up your corn tortillas in the same skillet or using a dry skillet over medium heat for about 30 seconds on each side until pliable and slightly charred.
Assemble the Tacos: Place slices of chicken in each tortilla then top generously with diced onions, chopped cilantro, and a squeeze of fresh lime juice before adding any additional toppings you desire.