In a bowl, combine chili powder, brown sugar, ground cinnamon, baking cocoa, salt, and pepper. Stir until well blended.

Generously rub the spice mixture all over the bone-in chicken breasts.

In a large skillet, heat together olive oil and balsamic vinegar over medium heat.

Add the chicken breasts and cook until beautifully browned, about 6-7 minutes on each side.

While the chicken is cooking, mix together melted butter, cilantro, red onion, lime juice, serrano pepper, and a touch of pepper in a bowl.

Once cooked, remove the chicken from the skillet and let it rest for a few minutes.

Top your cooked chicken with the cilantro lime butter just before serving.