Preheat oven to 375F. Line a baking sheet with parchment paper, if using. If not, spray with a light coating of nonstick cooking spray or use a silicon mat.
Wash, dry, peel if desired, and dice the potatoes into 1 ½ - 2 inch cubes. Cut the broccoli into florets. (The smaller the florets, the crispier they'll get.)
Open the pork loin package and pat the meat dry with a paper towel. Set aside.
Add the potatoes, broccoli, and carrots to a large bowl. Drizzle with the 3 T of olive oil. Add the 2 teaspoons of garlic powder, 1/2 t of salt, and 2 teaspoons Italian seasoning, then toss to coat.
Dump the potatoes and vegetables on the sheet pan then use clean hands or tongs to lay them flat and separated, leaving a rectangular space in the center.
Place the whole pork loin in the middle space.
Slide pan into the hot oven and bake for 40 minutes. Check doneness at 40 minutes: Use a meat thermometer to ensure the center temp is 145F. Add five minutes if needed and check temp again for doneness.
Remove the pan from the oven with hot pads, the allow everything to rest for 3 minutes or so. Use tongs to move the whole loin to a cutting board, then cut the pork loin into 1 ½ - 2 inch slices.
If meat is done but potatoes or carrots need a couple of minutes, leave them on the pan and roast for an additional 5 to 7 minutes.
Serve immediately.