Place the chicken in the slow cooker and season with black pepper.
In a medium bowl, combine soy sauce, honey, tomato paste, vinegar, garlic, ginger, sesame oil, 1 tablespoon water and sriracha.
Pour over the chicken and cook on LOW 3 to 4 hours.
Remove chicken, leaving the sauce in the slow cooker. Shred chicken with two forks; set aside.
In a small bowl, dissolve cornstarch in remaining ¼ cup water; add to the slow cooker and stir to combine.
Cover and cook on HIGH until slightly thickened, about 15 to 20 minutes; return chicken to the slow cooker and mix well.
Serve chicken and sauce over rice and top with sesame seeds and chopped scallions for garnish.
