In a medium bowl, whisk together lime juice, olive oil, minced garlic, cumin, chili powder, smoked paprika, dried oregano, salt, and pepper. Add the chicken thighs and ensure they are fully coated. Cover and let marinate for at least 30 minutes.

Preheat a grill or skillet over medium-high heat. Once hot, cook the chicken for 5-7 minutes on each side until cooked through, reaching an internal temperature of 165°F.

Transfer the chicken to a cutting board, let it rest for about 5 minutes, then slice into thin strips.

Warm the tortillas in a dry skillet for 20-30 seconds on each side until soft.

Assemble tacos with sliced chicken, chopped onions, fresh cilantro, and a squeeze of lime. Add optional toppings as desired.