In a bowl, combine lime juice, olive oil, minced garlic, ground cumin, chili powder, smoked paprika, dried oregano, salt, and black pepper. Mix well. Add the chicken thighs to the bowl and ensure they're fully coated in the marinade. Allow them to marinate for at least 30 minutes.
Preheat your grill over medium-high heat. Once hot, place the marinated chicken thighs on the grill. Cook for about 6–7 minutes per side or until they reach an internal temperature of 165°F (75°C).
While the chicken is grilling, chop your white onion and cilantro. Set aside in separate bowls.
Warm up the corn tortillas on the grill for about a minute on each side or wrap them in foil and place them in a preheated oven at low heat.
Slice the grilled chicken into bite-sized pieces and start assembling your tacos! Place some chicken on each tortilla and top with chopped onion and cilantro. Squeeze fresh lime juice over everything.