Preheat oven to 400 degrees F.
Spray a 9" x 13" baking dish with non-stick cooking spray. Unwrap the pork tenderloin and place it in the baking dish. Use a paper towel to pat dry the pork tenderloin, then season with salt and pepper.
In a small bowl, combine the room temperature butter, garlic, thyme, rosemary, sage, and onion powder and use a fork to mash and combine all of the ingredients. Using a spatula, spread this butter mixture evenly over the top of the pork tenderloin.
In a separate bowl, add the prepared onions, carrots, potatoes, avocado oil, and 1 teaspoon of reserved minced garlic. Stir until well coated, then arrange the veggies around the edge of the pork in the baking dish.
Roast in a preheated 400 degree oven for 35-40 minutes, or until the thermometer reads 145 degrees F. If the pork isn't golden brown on top, broil in the oven for a minute or two until golden.
Once the pork has reached 145 degrees, remove from the oven and let rest for about 10 minutes before slicing and serving.
To serve, spoon juices from the bottom of the baking dish over the meat. Slice the pork into 1" pieces, garnish with freshly chopped parsley and serve with some of the roasted vegetables and any other of your favorite sides. Enjoy!