Step 1: Prepare the Ingredients: Slice bell peppers, onion, carrots, and broccoli into bite-sized pieces. Mince garlic and set aside.
Step 2: Make the Teriyaki Sauce: In a small bowl, whisk together soy sauce, brown sugar or honey, water, rice vinegar, hoisin sauce, sesame oil, and ginger. Dissolve cornstarch in a small amount of water (about 1-2 tbsp) and add to the sauce, whisking until smooth.
Step 3: Assemble in the Crockpot: Place chicken breasts or thighs at the bottom of the crockpot. Layer sliced vegetables and garlic on top of the chicken. Pour the teriyaki sauce evenly over the chicken and vegetables.
Step 4: Slow Cook: Cover and cook on low for 4-5 hours or high for 2-3 hours, until chicken is fully cooked and vegetables are tender. About 15 minutes before serving, stir gently to coat everything evenly with sauce.
Step 5: Serve: Remove chicken and slice or shred as desired. Mix chicken back with vegetables and sauce in the crockpot. Serve hot over rice, noodles, or quinoa. Garnish with sesame seeds and sliced green onions.