01 - In a medium mixing bowl, whisk together the mayonnaise, lemon juice, olive oil, minced garlic, smoked paprika, dried oregano, salt, and black pepper until smooth and well combined.
02 - Pat the chicken breasts dry with paper towels and place them into a large resealable plastic bag or a shallow glass dish.
03 - Pour the marinade over the chicken, ensuring each breast is evenly coated on all sides. Seal the bag or cover the dish tightly and refrigerate for 1 to 4 hours.
04 - Preheat an outdoor grill or grill pan to medium-high heat, approximately 400°F. Lightly oil the grates to prevent sticking.
05 - Remove the chicken from the marinade, allowing any excess to drip off. Discard the remaining marinade. Place the chicken on the grill and cook for 6 to 8 minutes per side, until the internal temperature reaches 165°F and the juices run clear.
06 - Transfer the grilled chicken to a cutting board and let it rest for 5 minutes. Slice against the grain, garnish with fresh parsley or chives if desired, and serve immediately.