In a large skillet, heat the olive oil over medium-high heat. Add the onion, apples and sage. Saute until softened.
Remove from the heat and gently stir in the bread, egg, butter and salt and pepper. Add the chicken broth gradually until everything is moistened.
Let the stuffing mixture cool completely before putting it in the pork loin.
Spoon the stuffing down the pork, horizontally, in a line. Roll the pork over the stuffing, jelly roll style, ending with the seam down and fat side up.
Lightly score the fat, in a diamond pattern, with a sharp knife. Tightly tie the pork roast up with butcher's twine, season it with more salt and pepper, and transfer to a roasting pan.
Roast the pork in a preheated oven for about 90 minutes or until an instant-read thermometer registers 160°F Remove from the oven and let rest for 15 minutes before slicing. Garnish with apples and fresh herbs.