Add cubed chicken to a bag, add cornstarch, toss to coat. Put chicken in slow cooker.
In a separate bowl add soy sauce, orange juice concentrate, tomato paste, chicken broth, honey, garlic, ginger, orange zest, pepper, and salt. Stir together until combined. Pour over chicken in slow cooker. Either refrigerate until ready to cook, or begin cooking. Slow cook on high 4 hours or on low 6-8 hours.
After cooking time, stir and check for consistency. If the sauce is too thin, make a slurry by mixing about a tablespoon of cornstarch with about 1/4 cup water. Add slurry to the sauce and continue cooking for about 20 minutes. If the sauce is too thick, add chicken broth, orange juice (my favorite), or water until you get desired consistency.
Serve over rice. Garnish with sesame seeds and scallions.