Make marinade by combining lemon juice, olive oil, salt, pepper, and oregano. Place chicken in a dish with tall sides and pour marinade over chicken. Use spoon to baste chicken with marinade. Refrigerate for 2 to 24 hours--a longer marinade time will produce a more intense flavor. Remove from refrigerator and use a flat-sided utensil to gently scrape off any marinade solids. Grill chicken over high heat for a total of 20 minutes, turning over after first 10 minutes. Season with salt and pepper.