Prep the chicken: Trim any excess fat and cut the chicken into bite-size pieces, about 1 to 1.5 inches. Pat dry with paper towels for better browning and texture.

Mix the sauce: In a bowl, whisk together orange juice, orange zest, soy sauce, brown sugar, honey, rice vinegar, garlic, ginger, red pepper flakes, and sesame oil. If using orange marmalade, whisk it in now for a stronger orange note.

Load the slow cooker: Add the chicken to the slow cooker and pour the sauce over it. Stir to coat evenly.

Cook low and slow: Cover and cook on Low for 3.5–4.5 hours or on High for 2–2.5 hours. The chicken should be tender but not falling apart.

Thicken the sauce: In a small bowl, mix cornstarch with water to form a smooth slurry. Stir it into the slow cooker, turn heat to High, and cook for 15–20 minutes until the sauce thickens and becomes glossy.

Adjust to taste: Taste the sauce. Add a pinch of salt if needed, more vinegar for tang, or a drizzle of honey for sweetness. For a richer citrus punch, stir in a bit more zest at the end.

Finish and serve: Sprinkle with sliced green onions and sesame seeds. Serve over hot rice with steamed broccoli or snap peas on the side.