In a large bowl, whisk together the olive oil, Parmesan cheese, minced garlic, oregano, salt, black pepper, red pepper flakes (if using), and lemon juice until well combined.
Add the chicken breasts to the bowl, ensuring they are fully coated in the marinade. Cover and refrigerate for at least 30 minutes, or up to 4 hours for more flavor.
Preheat your grill to medium-high heat.
Remove the chicken from the marinade and let any excess drip off. Discard the remaining marinade.
Place the chicken on the grill and cook for 6-7 minutes per side, or until the internal temperature reaches 165°F.
Remove the chicken from the grill and let it rest for 5 minutes before slicing.