Heat the oven to 450 degrees F (230 degrees C). Line a large sheet pan with parchment paper and set aside.
To make the Pork Seasoning Rub, combine the Rubbed Sage (3 teaspoon), Kosher Salt (3 teaspoon), and Freshly Ground Black Pepper (1 1/2 teaspoon) together in a small bowl. Set aside a small amount for the vegetables.
Rub the Pork Tenderloin (1 pound) with the seasoning and set aside. You can refrigerate until you are ready to cook. You can even leave it in the fridge overnight.
Meanwhile chop the Butternut Squash (4 cup), Brussels Sprouts (4 cup), and Red Onion (1).
As you get the veggies chopped, add them to the parchment lined sheet pan. Season with salt, pepper, and a few pinches of the rubbed sage. Add a few teaspoons of Olive Oil (2 teaspoon) and toss to combine.
Spread the veggies out evenly and place the wire baking rack over the sheet pan.
Add the pork tenderloin to the baking rack and place in the oven. Bake for 10 minutes at 450 degrees F (230 degrees C).
Reduce the temperature to 375 degrees F (190 degrees C) and continue to roast for an additional 10 to 15 minutes or until the internal temperature reaches 145 degrees F (63 degrees C).
When the pork roast is thoroughly cooked, remove it from the oven. Place the pork tenderloin on a platter, cover it with foil, and let it rest for a minimum of 10 minutes.
Using tongs, give the veggies a quick toss and then return them to the oven. Continue to roast the veggies for another 10 to 15 minutes. They should be tender and golden brown on the edges.
Remove from the oven and serve immediately.