1. Set the bottom oven rack to the bottom 3 rd and a second rack to the top 3 rd . Preheat oven to 400°F and line two rimmed baking sheets with parchment paper or Silpat® baking mats. Set aside.
2. In a large bowl, toss the apple, fennel, red onion, sage, 2 tablespoons of olive oil, and balsamic vinegar. Season with salt and black pepper, to taste, and combine until the apple and veggies are completely coated.
3. Spread the apple mixture onto one of the prepared baking sheets and roast on the bottom oven rack for 10-15 minutes, or just until the veggies start to soften and develop a bit of color.
4. While the apples and veggies are roasting, place the pork tenderloin in the center of the second baking sheet and brush with the remaining olive oil. Generously season with salt and black pepper, to taste.
5. Once the apples and vegetables start to develop some color, place the seasoned pork tenderloin on the top oven rack and roast for 15 minutes before turning the pork. Cook tenderloin for another 10-15 minutes, or until it is cooked through.*
6. Remove both sheet pans from the oven and allow the pork to rest for 10 minutes before slicing and serving with the roasted apple and vegetables.
Enjoy!