Slice the chicken breasts in half and open them up to butterfly them (see the photo above).
Mix together the cream cheese, taco seasoning, and 3/4 cup cheddar cheese. Divide amongst the chicken breasts. Fold the chicken breast over on itself and secure closed with toothpicks (see photo above).
Add about a tablespoon of vegetable oil to the cast iron skillet and allow to heat up.
Add the chicken to the skillet and sear for about three minutes on each side.
Add the salsa to the top of the chicken, dividing evenly and then top with remaining cheese. Put in the oven (uncovered) and bake for about 20 minutes or until a thermometer registers 165 degrees in the thickest part of the chicken.
Remove the toothpicks, top with olives and jalapeños, and serve immediately.