Spray a 4 or 6-quart slow cooker with nonstick cooking spray, then add 2 pounds boneless skinless chicken thighs to the bottom of it.
Make the sauce by whisking ¾ cup packed brown sugar, 1 cup low-sodium soy sauce, 1 tablespoon sesame oil, 2 tablespoons minced garlic, 1 ½ tablespoons grated fresh ginger, 1 tablespoon rice vinegar, and 1 tablespoon gochujang chili paste together in a medium bowl. Pour the sauce over the chicken and toss to coat the thighs.
Cover and cook on LOW for 4-5 hours or on HIGH for 3-4 hours.
Use two forks to shred the chicken in the slow cooker. Whisk together 2 tablespoons cornstarch and 2 tablespoons water in a small bowl, then add to the slow cooker and stir to incorporate. Cover and cook for 20-30 minutes, until the sauce thickens.
Serve over warm rice and garnish with green onions and sesame seeds.
