01 - Whisk together lime juice, lime zest, olive oil, garlic, chili powder, cumin, smoked paprika, salt, and black pepper in a large bowl. Add chicken breasts and turn to coat evenly. Cover and refrigerate for at least 20 minutes, up to 2 hours.
02 - Preheat a grill or skillet to medium-high heat. Remove chicken from the marinade and discard excess. Grill or sear for 6 to 7 minutes per side until cooked through, reaching an internal temperature of 165°F.
03 - While the chicken cooks, combine diced avocados, tomato, red onion, cilantro, lime juice, and salt in a bowl. Gently toss to combine without mashing the avocado.
04 - Transfer cooked chicken to serving plates. If using cheese, sprinkle it over the hot chicken so it melts slightly.
05 - Top each chicken breast with a generous spoonful of the avocado mixture. Finish with lime wedges and extra cilantro. Serve immediately.