01 - In a large mixing bowl, whisk together the mayonnaise, lemon juice, minced garlic, Dijon mustard, smoked paprika, dried oregano, salt, and black pepper until a smooth, uniform paste forms.
02 - Add the chicken breasts to the bowl and turn to coat each piece thoroughly in the marinade. Cover tightly and refrigerate for at least 2 hours, or overnight for the most deeply developed flavor.
03 - Preheat an outdoor grill or grill pan to medium-high heat, targeting roughly 400°F. Brush the grates with olive oil to prevent sticking.
04 - Remove the chicken from the marinade, letting any excess drip off. Place the breasts on the hot grill and cook for 6 to 8 minutes per side, until the internal temperature registers 165°F and the juices run clear.
05 - Transfer the grilled chicken to a cutting board or platter and allow it to rest for 5 minutes before slicing or serving to lock in the juices.