In a large mixing bowl, combine brown sugar, balsamic vinegar, soy sauce, garlic, Dijon mustard, black pepper, and salt. Whisk until well blended.
Heat olive oil in a skillet over medium heat. Sear the pork tenderloin for about 2-3 minutes on each side until browned. This step enhances the flavor but can be skipped if you prefer a quicker method.
Transfer the seared pork tenderloin into your crockpot. Pour the brown sugar balsamic mixture over the pork, ensuring it's evenly coated.
Cover the crockpot and cook on low for 6 hours or until the pork is tender and an internal temperature of 145°F is reached.
Once cooked, remove the pork from the crockpot and let it rest for 5 minutes before slicing.
Serve the sliced pork glazed with the remaining sauce from the crockpot. Garnish with fresh parsley if desired.
For added depth of flavor, consider adding sliced onions or mushrooms to the crockpot before cooking.
Store any leftovers in an airtight container in the refrigerator for up to 3 days.