In a bowl, whisk together olive oil, lemon juice, garlic, oregano, salt, and pepper.
Place chicken in a large resealable bag or bowl and pour marinade over it.
Seal the bag or cover the bowl and refrigerate for at least 30 minutes.
Preheat the grill or oven to 375°F (190°C).
Remove chicken from the marinade and discard the remaining marinade.
Place chicken on the grill or a baking sheet.
Grill for 20-25 minutes or bake for 30-35 minutes, turning halfway through.
Check internal temperature; it should reach 165°F (75°C).
Remove chicken from heat and let it rest for 5 minutes.
Garnish with fresh parsley, feta, and olives before serving.