In a ziplock bag, add the chicken breasts and sprinkle in cornstarch, sealing the bag tightly. Shake vigorously until each piece is evenly coated without any clumps.

Heat a tablespoon of vegetable oil in a skillet over medium-high heat. Once the oil shimmers, add the coated chicken pieces and brown for about 2 minutes on each side.

Carefully transfer the lightly browned chicken into your slow cooker, ensuring even distribution.

In a medium bowl, whisk together the hoisin sauce, rice wine vinegar, light brown sugar, and sesame oil until well blended and smooth.

Pour the sauce mixture over the chicken in the slow cooker, ensuring each piece is generously coated.

Cover your slow cooker and set it to low heat for 2 to 3 hours.

Once cooking is complete, garnish the chicken with freshly chopped green onions and a sprinkle of sesame seeds before serving.