Heat the olive oil in a large skillet over medium-high heat.
Add the chicken thighs and cook for about 5-7 minutes on each side, or until cooked through and golden brown.
Remove from the skillet and let rest for a few minutes before slicing into thin strips.
In a small bowl, mix together the chili powder, cumin, garlic powder, onion powder, smoked paprika, salt, black pepper, and cayenne pepper (if using).
Sprinkle the spice mixture over the sliced chicken and toss to coat evenly.
In the same skillet, warm the corn tortillas for about 30 seconds on each side until pliable.
To assemble the tacos, place a portion of the spiced chicken on each tortilla.
Top with chopped cilantro and diced onion.
Serve with lime wedges and your choice of salsa or hot sauce.