Preheat the oven to 400°F (200°C).
Line a large baking sheet with foil or lightly grease it with oil.
Pat the pork loin dry using paper towels.
In a small bowl, mix olive oil, Dijon mustard, honey, apple cider vinegar, garlic, thyme, rosemary, paprika, salt, and black pepper.
Rub the seasoning mixture evenly over the pork loin.
Place the pork loin in the center of the prepared baking sheet.
In a large bowl, toss Brussels sprouts, apples, and onion with olive oil, salt, and pepper.
Arrange the vegetables and apples around the pork loin in an even layer.
Roast uncovered for 40–45 minutes, turning the vegetables halfway through.
If the pork browns too quickly, loosely cover it with foil.
Continue roasting until the internal temperature of the pork reaches 145°F (63°C).
Remove the pan from the oven and let the pork rest for 10 minutes before slicing.
Slice the pork and serve with roasted Brussels sprouts and apples.