This Caramelized Onion Focaccia Chicken Sandwich is made with with the Trader Joe’s French onion focaccia and… wow.
This is not just a chicken sandwich. The bread is already layered with that deep onion flavor, then you add sautéed mushrooms, Gruyère, mustard aioli, and melty mozzarella, and suddenly it tastes like a French onion soup and a grilled cheese had a very good idea.
A Quick Look at the Recipe
✅ Recipe Name: Caramelized Onion Focaccia Chicken Sandwich
🕒 Ready In: 20 minutes
👪 Serves: 6
🍽 Calories: ~ 277 per serving (estimated)
🥣 Main Ingredients: Chicken, Focaccia, Gruyere, Mozarella, Mushrooms, Arugula
👌 Difficulty: Easy
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It’s warm, savory, a little sharp from the mustard, earthy from the mushrooms, and finished with fresh arugula so it doesn’t feel heavy. This is one of those “why is this so good?” sandwiches that you’ll absolutely make again.
If you are on a sandwich kick, check out my Baked Chicken Caesar Sandwich or this Viral Doner Kebab Sandwich!
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Why You’ll Love This Recipe
That bread does half the work. French onion focaccia already brings serious flavor.
Savory and melty. Gruyère + mozzarella is elite sandwich behavior.
Balanced. Rich cheese, earthy mushrooms, bright arugula.
Quick but impressive. Feels gourmet, takes very little effort.
Caramelized Onion Focaccia Chicken Sandwich Video
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Ingredient Notes
Trader Joe’s French onion focaccia: Soft inside, crisp when toasted, and already packed with caramelized onion flavor.
Cooked chicken: Makes this hearty and satisfying; rotisserie works beautifully.
Mushrooms: Add earthy depth that pairs perfectly with Gruyère.
Garlic: Boosts the mushroom flavor without overpowering.
Gruyère: Nutty and slightly sharp, melts beautifully and gives French onion vibes.
Mozzarella: Adds that gooey, stretchy melt factor.
Mustard aioli: Brings creaminess and tang that cuts through the richness. If you don't live near a Trader Joe's, just combine mayo and mustard.
Arugula: Fresh, slightly peppery contrast that keeps the sandwich from feeling too heavy.
Instructions
Full recipe and instructions in the recipe card at the end of post
Step 1: Slice the focaccia and toast until lightly crisp.
Step 2: Sauté mushrooms with garlic and seasoning.
Step 3: Spread mustard aioli over the toasted bread.
Step 4: Layer chicken and cheeses evenly.
Step 5: Melt until the cheese is bubbly and gooey.
Step 6: Top with mushrooms and arugula, then close and slice.
Substitutions & Variations
No Gruyère? Use provolone or Swiss.
No mushrooms? Skip them or add caramelized onions.
More indulgent? Add a little butter to the outside before pressing.
Spicier? Add a swipe of Dijon or cracked black pepper.
FAQ
Yes, just cook it fully before assembling the sandwich.
Absolutely. A panini press makes it extra crisp.
Best fresh, but you can prep the mushrooms and chicken ahead of time.
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⭐️ Recipe
Caramelized Onion Focaccia Chicken Sandwich
Ingredients
- 1 Trader Joe’s French Onion Focaccia sliced
- 1½ cups cooked chicken sliced or shredded
- 1 cup mushrooms sliced
- ¼ teaspoon salt
- ¼ teaspoon onion powder
- ¼ teaspoon dried oregano
- 1 garlic clove crushed
- 1 tablespoon extra virgin olive oil
- ⅓ cup Gruyère cheese shredded
- ¼ cup shredded mozzarella
- ⅓ cup arugula
- 3 tablespoon mustard aioli or Dijon + mayo mixed together
Instructions
Toast the Bread
- Preheat oven to 375°F.
- Slice the focaccia horizontally and place cut-side up on a baking sheet.1 Trader Joe’s French Onion Focaccia
- Toast for about 10 minutes, until lightly crisp on the edges but still soft inside.
Cook the Mushrooms
- Heat olive oil in a skillet over medium heat.
- Add sliced mushrooms and cook for 3–4 minutes until they release moisture.1 cup mushrooms, 1 tablespoon extra virgin olive oil
- Stir in garlic, salt, onion powder and cook until mushrooms are tender and lightly golden.¼ teaspoon salt, 1 garlic clove, ¼ teaspoon onion powder
Assemble and Melt
- Spread mustard aioli evenly over the toasted focaccia.3 tablespoon mustard aioli
- Layer cooked chicken over the bottom half.1½ cups cooked chicken
- Sprinkle Gruyère, oregano, and mozzarella evenly on top.⅓ cup Gruyère cheese, ¼ cup shredded mozzarella, ¼ teaspoon dried oregano
- Return to the oven or place in a skillet and cook until the cheese is fully melted and bubbly.
Finish
- Top with sautéed mushrooms and a handful of fresh arugula.⅓ cup arugula
- Close the sandwich, slice, and serve warm.
Video
Notes
Storage & Reheating
- Refrigerate: Store wrapped for up to 2 days.
- Reheat: Warm in a skillet or oven to re-crisp. Avoid the microwave.
Zackery A. says
I saw this idea appear on my feed a few times. I do like your Mediterranean twist on it though. Even though it was tasty, I just don't trust the Trader Joe's quality sometimes, as they add a lot of additives.