Peel the squash, slice in half lengthwise and remove the seeds. Cut into 1/2-inch slices and place in a roasting pan. Drizzle with olive oil, salt, and pepper. Mix to evenly coat the squash with the oil and spread in an even layer. Add the thyme sprigs. Roast in the preheated oven until the squash just begins to become tender, 20 minutes.
While the squash is roasting, prepare the tenderloin. In a small bowl, combine the salt, pepper, garlic powder, onion powder, and cinnamon. Stir to combine and sprinkle all over the dry tenderloins. Rub into the meat, picking up any fallen bits.
In a large 12-inch skillet, heat the olive oil over medium-high. Once the oil is shimmering and hot, sear the tenderloin until browned all around, about 3-5 minutes on all four sides. Remove from heat and set aside.
Cut apples into quarters and remove the core. After removing the core, cut each quarter in half again.
When the squash is just beginning to become tender, remove from the oven and add the apples. Stir to combine and spread in even layer. Add seared tenderloin on top of squash and apples, adding any juice that gathered under the meat.
Continue to roast until the apples are tender and the pork registers 145°F, about 20 minutes. Remove from oven and let rest for 10 minutes.
While resting, prepare pan sauce. Heat skillet over medium-high for 2 minutes. Add apple cider and bring to a boil. Turn down to a simmer and scrape the browned bits from the bottom. When the apple cider is reduced by half, about 3 minutes, turn off the heat and whisk in the Dijon mustard and butter. Whisk until smooth.
Cut pork and pour the pan sauce over the cut pieces. Serve with the squash and apples.