In a mixing bowl, whisk together the olive oil, lemon juice, minced garlic, dried oregano, fresh parsley, salt, and black pepper.
Place the chicken breasts in a baking dish and pour the marinade over them, ensuring the chicken is well coated. Cover and marinate in the refrigerator for at least 30 minutes (or up to 2 hours for stronger flavor).
Preheat the oven to 375°F (190°C).
Once marinated, remove the chicken from the refrigerator and let it sit at room temperature for about 10 minutes.
Bake the chicken in the preheated oven for 25-30 minutes, or until the chicken is fully cooked (internal temperature should reach 165°F or 75°C).
Remove the chicken from the oven and let it rest for 5 minutes before slicing.
Garnish with additional fresh parsley and lemon slices, if desired, and serve warm.