Preheat your oven to 400°F (200°C). Place your baking sheet in the oven to heat up too.
Cut your Brussels sprouts, carrots, and apples. Toss them in a bowl with half of the olive oil, half of the minced garlic, and a splash of red wine vinegar. Season with salt and pepper.
In another bowl, combine the remaining olive oil, Dijon mustard, lemon zest, chopped rosemary, thyme, oregano, sage, smoked paprika, and remaining minced garlic. If using, add red pepper flakes. Rub this mix all over your pork loin.
Carefully remove the hot baking sheet from the oven. Spread your seasoned veggies and apples evenly, making room for the pork loin in the center. Place pork on the sheet.
Put the sheet back in the oven and roast for about 45-50 minutes, or until a meat thermometer reads 145°F (63°C) for the pork.
Let the pork rest for 5 minutes before slicing. Drizzle lemon juice over everything for that extra kick of flavor. If using, scatter a few slices of onion for added aroma and taste.
Cut the pork against the grain for tender slices and serve it up with your perfectly roasted veggies and apples.
Notes
Prep Ahead: Chop all your veggies and apples earlier in the day or even the night before. Makes the actual cooking part a breeze.
Room Temp Pork: Take the pork out of the fridge about 30 minutes before cooking. It helps it cook more evenly.
Hot Oven, Hot Pan: Preheat your baking sheet in the oven while it's warming up. It gives everything a nice little sear as soon as it hits the pan.
Herb Hack: No fresh herbs? Use dried ones, but cut the quantity by a third. They're more concentrated, so you don't need as much.
Tongs Are Your Friend: Use tongs to flip the pork and veggies halfway through for even cooking and browning. Fingers are for eating, not for burns!
Check for Hotspots: All ovens have 'em. If one side of your sheet is cooking faster, just rotate the pan halfway through.
Juice Boost: Squeeze a lemon or drizzle some extra olive oil over everything right when it comes out of the oven. You'll thank me later.
Slice Thin: When you're finally ready to dig in, slice the pork thinly against the grain. Makes for a tender bite.