Mix the rosemary, garlic, mustard, salt and pepper in a small bowl. Rub the mixture evenly over the pork; place in a shallow dish. Let stand at room temperature for 15 minutes or in the refrigerator for up to 2 hours.
Brown the pork on all sides in heated olive oil in a skillet. Place in a baking pan.
Bake at 400 degrees for 20 minutes or until cooked through.