Peel apple, quarter, and remove core. Cut into ¼" dice. Peel and mince shallot. Stem sage. Cut twine into five equal pieces. Place pork tenderloin on a separate cutting board. Hold knife blade parallel to the board and make a lengthwise cut through the center. Stop ¼" short of opposite edge of tenderloin so pork remains in one piece. Open meat as you would a book. Cover with plastic wrap and pound out to a uniform ¼" thickness. Season both sides with ¼ tsp. salt and a pinch of pepper.
Cook Filling and Stuff Pork
Place a large non-stick pan over medium heat. Add 1 tsp. olive oil, half the apple(reserve remaining for sauce), and half the shallot (reserve remaining for vegetables) to hot pan. Stir occasionally until shallot is translucent, 1-3 minutes. Add cranberries and half the Dijon (reserve remaining for sauce). Stir occasionally until apples slightly soften, 1-2 minutes. Remove from burner, let cool 3 minutes, and season with a pinch of salt and pepper. Place ½ cup filling down center of tenderloin and roll. Any leftover filling can be served on the side. Tie pork tenderloin closed with twine. Wipe pan clean and reserve.
Cook Pork and Crisp Sage
Return pan used to cook filling to medium-high heat. Add 1 tsp. olive oil and tenderloin to hot pan. Cook until browned on all sides, 5-6 minutes. Transfer to prepared baking sheet and roast until pork reaches a minimum internal temperature of 145 degrees, 10-12 minutes. Rest at least 5 minutes. Line a plate with a paper towel. While pork roasts, place a small non-stick pan over medium-high heat. Add 2 Tbsp. olive oil and sage to hot pan. Stir occasionally until sage is crispy, 2-3 minutes. Remove to towel-lined plate. Reserve 2 tsp. sage olive oil. Wipe pan clean and reserve.
Cook Vegetables and Make Sauce
Return pan used to sear pork with reserved sage olive oil to medium-high heat. Add butternut squash to hot pan and stir occasionally 5 minutes. Add remaining shallot and stir occasionally until squash is tender, 1-2 minutes. Season with a pinch of salt and pepper. While vegetables cook, return pan used to crisp sage to medium heat. Add remaining apples, base, remaining Dijon, ¼ cup water, and any accumulated juices from resting pork to hot pan. Stir occasionally until apples soften, 3-4 minutes. Remove from burner, then mash into a coarse consistency like a chunky apple sauce.
Finish the Dish
Slice pork, place on a plate, and top with sauce. Serve vegetables alongside. Crumble crispy sage over vegetables.