Prep the chicken: Trim and cut chicken into 1-inch pieces. Pat dry with paper towels for better browning and texture.
Make the sauce: In a bowl, whisk together soy sauce, honey, ketchup, rice vinegar, hoisin (if using), garlic, ginger, sesame oil, red pepper flakes, and chicken broth.
Load the slow cooker: Add chicken to the slow cooker.
Pour the sauce over the top and toss to coat. If adding bell peppers, stir them in now for soft, saucy peppers; or save them for later if you prefer them crisp-tender.
Cook low and slow: Cover and cook on Low for 3–4 hours or High for 1.5–2 hours, until the chicken is cooked through and tender. Avoid overcooking to keep the chicken juicy.
Thicken the sauce: Stir together cornstarch and water.
Uncover the slow cooker, stir in the slurry, and cook on High for 15–20 minutes until the sauce thickens. If you held back the bell peppers, add them now so they soften slightly as the sauce thickens.
Add the cashews: Stir in cashews during the last 10 minutes so they warm and soak up flavor but stay crunchy. Reserve a few for topping.
Taste and adjust: Add a splash of vinegar for brightness, more honey for sweetness, or soy sauce for salt.
Balance is key.
Serve: Spoon over hot rice, sprinkle with green onions and sesame seeds, and finish with extra cashews for crunch.