Place chicken breasts in crockpot in a single layer. Pour teriyaki sauce over chicken, coating each piece.
Cover and cook on LOW for 6 hours or on HIGH for 3 to 4 hours. Avoid lifting lid during cooking.
Add broccoli florets during the last 30 minutes of cooking, pressing them slightly into the sauce.
Check that chicken reaches 165°F internal temperature in the thickest part. Shred with forks or serve whole. Spoon sauce over chicken and broccoli, then serve hot over rice or noodles.
Notes
For thicker sauce, remove lid during last 30 minutes or make cornstarch slurry (1 tablespoon cornstarch + 2 tablespoons water) and stir in at end.
Fresh or frozen broccoli both work. No need to thaw frozen.
Chicken thighs can be substituted for juicier results with same cooking times.
Each time you lift the lid adds 15-20 minutes to cooking time.