Spray the bottom of the slow cooker with non-stick cooking spray and add 4 boneless skinless chicken breasts.
In a small mixing bowl add 3 tablespoons soy sauce, ½ cup brown sugar, 3 tablespoons lemon juice, 2 tablespoons Worcestershire sauce, 1 tablespoon grated ginger, ¼ teaspoon red pepper flakes, ¼ teaspoon minced garlic, and ⅛ teaspoon pepper. Whisk to combine and pour the sauce over the chicken.
Cook on LOW for 4-6 hours or HIGH for 3-4 hours. Once done cooking, remove the chicken from the slow cooker and shred using two forks.
To thicken the sauce, pour the liquid from the slow cooker into a small saucepan. Whisk in 1 tablespoon cornstarch into the sauce. Bring to a boil over medium-high until it starts to thicken up.
Serve over rice and top with the sauce. Garnish with sesame seeds and green onions, if desired.