Spray the inside of large slow cooker lightly with nonstick spray. Trim fat from pork loin, if desired, and pat dry with paper towels (see note).
In a small bowl, combine ½ cup brown sugar, mustard, 1 tablespoon balsamic vinegar, garlic, salt and pepper. Rub mixture on all sides of the pork loin and put the meat into the prepared slow cooker.
Cook, covered, on high for 4 hours, or on low for 7-9 hours.
For the Glaze:
When pork has finished cooking, turn off heat to let pork rest, and begin glaze.
In a small saucepan, whisk together sauce ingredients: 1 cup brown sugar, cornstarch, ½ cup balsamic vinegar, water, soy sauce, and black pepper. Bring to a boil over medium-high heat, reduce to a simmer (medium-low heat), and simmer until thickened, 10 to 15 minutes. Stir occasionally.
Cut pork into thick slices, about 1 inch thick. Drizzle glaze over pork and garnish with sesame seeds and green onions. Alternatively, shred the pork with two forks and mix with glaze.
If desired, season pork with salt and pepper and sear on all sides in a large skillet or Dutch oven before placing in slow cooker and adding the rub.
Leftover pork will keep in the refrigerator for three to four days or in the freezer for two to three months.
Oven roasted pork loin: You'll need a large roasting pan; prep the roast as directed. Preheat the oven to 375°F and roast the pork for one to two hours, depending on the size of the roast (internal temperature should be at least 145°F). If it's browning too much, cover the pan with foil. Let pork rest for 10 to 15 minutes before slicing. Serve with glaze.