Heat a large skillet on medium-high heat and add the avocado oil.
Liberally season the pork loin with the kosher salt and fresh ground pepper. Sear the pork on all sides until browned - about 3-4 minutes per side.
Once the searing is complete, remove the skillet from the heat and place it on a plate.
Carefully add the onions, garlic, apples to the skillet. The idea here is create a bed for the pork loin to sit on. The garlic goes cut side down with the apples and onions.
Return the pork loin to the skillet and gently place it onto its apple/onion/garlic bed. In small mixing bowl or cup, mix together the ground sage, Worcestershire sauce, Dijon mustard, and maple syrup. Drizzle this over the pork loin.
Place the skillet into a preheated 375° oven for approximately 25-30 minutes. Carefully, add in the halved Brussels sprouts, evenly distributing them around the pork loin, apples, and onion.
Continue roasting for an additional 20-25 minutes, pulling it from the oven when the meat reaches 135°F-140°F.
Tent the pork with foil and let it rest until the final temperature is 145°F.
Slice the pork, drizzle the pan sauce, and enjoy!
Notes
The roasted garlic cloves will be very caramelized and wonderful at the end of the roasting period. I suggest smashing them into the pan sauce.