In a mixing bowl, combine the oregano, lavender, thyme, rubbed sage, marjoram, rosemary, salt, lemon juice, olive oil, minced garlic, and minced onion; whisk until thoroughly mixed.
Trim excess fat and cartilage from the chicken breasts, then pound or slice them to an even 1/2-inch thickness so they cook quickly and evenly.
Place the chicken in a resealable plastic bag and pour in the marinade; seal the bag and massage it so the chicken is evenly coated. Refrigerate and marinate for 1 hour.
Heat a cast-iron pan over medium-high heat until hot. Transfer the chicken directly from the bag to the pan, keeping any herbs and onion that cling to the meat.
Sear the chicken on each side until cooked through and an internal temperature of 165°F (74°C) is reached, about a few minutes per side depending on thickness.
Remove from the pan and let rest briefly before serving.
