Make the marinade: In a small bowl, whisk together olive oil, lime juice, lime zest, chili powder, cumin, smoked paprika, garlic powder, salt, and black pepper.
Marinate the chicken: Place chicken in a resealable zip‑top bag or shallow dish. Pour marinade over chicken, ensuring it’s evenly coated. Seal or cover and refrigerate for at least 15–30 minutes (or up to 4 hours).
Prep the salsa: In a medium bowl, gently combine diced avocados, tomatoes, red onion, jalapeño (if using), cilantro, lime juice, salt, and pepper. Set aside.
Cook the chicken (grill method): Preheat grill to medium‑high heat. Remove chicken from marinade and discard excess. Grill for 6–7 minutes per side, or until internal temperature reaches 165°F (74°C).
Cook the chicken (stovetop method): Heat a large skillet over medium‑high heat with a drizzle of oil. Add chicken and cook 6–7 minutes per side, until golden and cooked through (165°F / 74°C internally).
Rest and slice: Transfer chicken to a cutting board and let rest for 5 minutes. Slice against the grain into thin strips or bite‑sized pieces.
Serve: Warm tortillas if using. Serve chicken with avocado salsa, shredded lettuce, cheese, sour cream, and lime wedges for a complete taco night.