In a large mixing bowl, combine the lemon juice, lemon zest, olive oil, minced garlic, dried oregano, salt, black pepper, and red pepper flakes. Whisk together until well blended.
Add the chicken breasts to the marinade, ensuring they are fully coated. Cover the bowl with plastic wrap and refrigerate for at least 30 minutes (or up to 2 hours for more flavor).
Preheat your grill or grill pan over medium-high heat.
Remove the chicken from the marinade, allowing excess marinade to drip off. Discard the remaining marinade.
Place the chicken on the grill and cook for about 6-7 minutes on each side, or until the internal temperature reaches 165°F (75°C) and the chicken is nicely charred.
Remove the chicken from the grill and let it rest for 5 minutes. This will keep it juicy.
Slice the chicken and serve it warm, garnished with freshly chopped parsley and lemon slices.