Marinate the chicken by combining olive oil, chili powder, cumin, garlic powder, onion powder, smoked paprika, salt, and pepper in a bowl. Add chicken thighs and coat well. Let marinate for at least 20 minutes.
Preheat grill or skillet over medium-high heat. Cook marinated chicken for 5-7 minutes on each side until fully cooked (internal temperature of 165°F). Let rest for a few minutes.
Warm corn tortillas in a dry skillet for about 30 seconds on each side. Chop cilantro and dice onion while tortillas warm.
Slice cooked chicken into strips. Assemble tacos by placing chicken in tortillas and topping with onion, cilantro, and a squeeze of lime. Add salsa or hot sauce if desired.