Season all sides of pork loin roast generously with salt and pepper.

Place cut onions in the bottom of your slow cooker.

Heat a large skillet over medium-high heat. Add oil and sear pork loin on all sides until golden brown, 2 minutes per side. Remove from pan and place on top of onions in slow cooker.

Turn off the heat on your skillet and add garlic, water, balsamic vinegar and soy sauce. Stir together ingredients, making sure to scrape up any brown bits that stuck to the pan.

Sprinkle brown sugar on top of pork loin and then pour sauce mixture over the pork.

Cover and cook on Low for 5-6 hours, or until the internal temperature is 145 degrees Fahrenheit.

Once cooked, remove pork loin to a plate and cover with foil. Allow to rest for 10 minutes.

While pork is resting, pour the sauce and juices from the slow cooker into a saucepan. Bring to a simmer over medium heat and allow the sauce to thicken, 5-6 minutes. Stir occasionally.

Slice your pork loin against the grain to ensure maximum tenderness.