French Onion Chicken Sandwich

Get ready to fall head over heels for the ultimate comfort food mashup!

This French Onion Chicken Sandwich takes everything you love about that classic soup and transforms it into the most satisfying sandwich you’ll ever sink your teeth into.

We’re talking deeply caramelized onions that have been cooked to golden perfection, juicy grilled chicken, and melted Swiss cheese that gets all bubbly and irresistible.

The magic happens when those sweet, jammy onions meet the smoky grilled chicken and that nutty Swiss cheese starts to melt.

Every bite delivers layers of flavor that’ll make you wonder why you haven’t been making this your whole life.

The best part?

Those caramelized onions can be made up to three days ahead, so you’re basically halfway to sandwich heaven before you even start grilling.

Ingredients

For the Caramelized Onions:

• 1 tablespoon extra virgin olive oil
• 1 large white onion, thinly sliced
• 1 teaspoon granulated sugar

For the Chicken:

• 2 boneless, skinless chicken breasts, halved crosswise and pounded to 1-inch thickness, if necessary
• Nonstick cooking spray

For Assembly:

• 4 slices Swiss cheese
• 4 hamburger buns
• 2 cups baby spinach

Steps

1. In a large skillet, heat oil over medium heat. Add the sliced onion and sugar, then cook for 25 minutes or until onions are deeply caramelized, stirring frequently. You’ll know they’re perfect when they turn a rich golden-brown color and become jammy in texture. The sugar helps speed up the caramelization process and adds extra depth of flavor. This step can be done up to 3 days in advance – just store them covered in the refrigerator and re-warm in the microwave for 30-45 seconds or in a small pan on the grill before proceeding.
2. Preheat your grill for direct grilling over medium-high heat (around 375-400°F or 190-204°C). While the grill heats up, spray the chicken pieces generously with nonstick cooking spray on both sides. This prevents sticking and helps create those beautiful grill marks you want.
3. Transfer the chicken to the hot grill rack, cover, and cook for 10 minutes or until the chicken loses its pink color throughout and the internal temperature reaches 160°F (71°C), turning once halfway through. Use an instant-read thermometer inserted into the thickest part of the chicken to check – this ensures perfectly cooked, juicy chicken every time.
4. Place the Swiss cheese slices on top of the chicken pieces while they’re still on the grill. Cover and cook for 1-2 minutes or until the cheese is completely melted and starts to turn golden brown around the edges. The residual heat from the chicken will help melt the cheese beautifully, creating that perfect stretchy, gooey texture.
5. Build your sandwiches using the hamburger buns as your base. Layer with the baby spinach first (this creates a barrier to prevent the bun from getting soggy), then add the cheesy chicken pieces, and finally top with those gorgeous caramelized onions. The contrast between the fresh spinach, savory chicken, nutty cheese, and sweet onions creates the perfect bite every time.

Smart Swaps

• Gruyère cheese instead of Swiss (1:1 ratio) – adds a nuttier, more complex flavor
• Arugula instead of spinach – provides a peppery bite that complements the sweet onions
• Brioche buns instead of regular hamburger buns – adds richness and holds up better to the juicy fillings

Make It Diabetes-Friendly

Replace the granulated sugar with 1/2 teaspoon stevia or monk fruit sweetener when caramelizing onions – reduces carbs by 4g per serving. Use whole grain buns instead of regular hamburger buns to add 3g fiber and reduce the glycemic impact. Consider serving as an open-faced sandwich using only the bottom bun to cut carbs by approximately 15g per serving. The protein from the chicken and fat from the cheese naturally help slow glucose absorption. Pair with a small side salad instead of fries to keep the meal balanced and blood sugar stable.

Pro Tips

• Slice onions with the grain (from root to tip) for better caramelization – they hold their shape better during the long cooking process
• Let chicken rest for 3-5 minutes after grilling before assembling – prevents juices from making the bun soggy
• Toast the buns cut-side down on the grill for 30-60 seconds for extra flavor and structure