Add the olive oil, lemon juice, garlic, oregano, salt, and pepper to a large zip top bag, or a large shallow dish. Close the bag and massage to combine the ingredients, or stir the ingredients in the dish until combined.
Filet each chicken breast into two thinner pieces. Place the pieces in the bag or dish, making sure the chicken pieces are completely covered in marinade. Marinate the chicken for 30 minutes up to 8 hours, turning occasionally to maximize the chicken’s contact with the marinade.
When ready to cook, heat a large skillet over medium flame. Transfer the chicken from the marinade to the hot skillet and cook on each side until well browned and cooked through (about 5-7 minutes each side, depending on the size of the pieces). I cooked two pieces at a time to avoid over crowding the skillet, which can cause juices to pool and prevents browning. Discard the excess marinade.
Transfer the cooked chicken from the skillet to a cutting board and let rest for five minutes before slicing and serving.