Prepare the slow cooker with nonstick cooking spray.
Place half of the onions into the bottom of the slow cooker. Top with the chicken breasts.
In a mixing bowl, combine broth and Worcestershire sauce.
Over the chicken breasts, add the remaining onion, onion soup mix, and sauce mixture.
Cover the slow cooker and cook on low for about 5-6 hours or until the chicken is cooked through and tender.
When the chicken is cooked through, top each chicken breast with a generous amount of shredded Gruyere or Swiss cheese. Replace the lid until the cheese melts.
Serve the French onion chicken hot, garnished with fresh parsley if desired.
Notes
Please note that the nutritional information provided is an estimate based on the ingredients listed and may vary according to specific brands used, substitutions, and serving size. For the most accurate dietary information, consider consulting with a professional nutritionist.