1. Caramelize the Onions

• Start by heating 1 tablespoon of olive oil and 1 tablespoon of butter in a large skillet over medium heat. Add the sliced onions and a pinch of salt, stirring to coat the onions evenly in the oil and butter.
• Cook the onions slowly, stirring occasionally, for about 15-20 minutes. Allow the onions to become soft, golden, and caramelized. If the onions begin to brown too quickly or stick to the pan, add a splash of vegetable broth to deglaze the pan.
• Once the onions are caramelized, add ½ cup of vegetable broth and the thyme. Stir to combine, and cook for an additional 3-4 minutes, letting the broth reduce and infuse the onions with flavor. If you like a slightly sweeter taste, drizzle in a small amount of balsamic vinegar at this point.
• Remove the caramelized onions from the skillet and set them aside.

2. Sauté the Vegetables

• In the same skillet, add the remaining 1 tablespoon of olive oil and heat over medium heat. Add the garlic, bell pepper, and zucchini to the skillet. Sauté for about 4-5 minutes until the vegetables are softened and slightly browned. If you are using mushrooms, add them to the pan and sauté for an additional 2-3 minutes until tender.
• Season the sautéed vegetables with salt and pepper, adjusting to taste. Remove from heat and set aside.

3. Toast the Baguette or Sub Rolls

• Preheat your oven to 375°F (190°C).
• Slice the baguettes or sub rolls in half, lengthwise. Place the cut side of the bread face-up on a baking sheet. Toast in the preheated oven for about 5-7 minutes, or until the bread is golden and slightly crispy.
• Once toasted, remove the rolls from the oven and set aside.

4. Assemble the Veggie Subs

• Start by placing a generous layer of caramelized onions on the bottom half of each toasted baguette or sub roll.
• Top the onions with a portion of the sautéed vegetables, spreading them evenly.
• Sprinkle the shredded Swiss cheese or Gruyère generously over the vegetables. If you’re using provolone or mozzarella cheese for extra melt, add it on top of the Swiss cheese.
• Place the sandwiches under the broiler for 2-3 minutes, or until the cheese is melted and bubbly. Be sure to keep an eye on them so the bread doesn’t burn.

5. Serve

• Remove the subs from the oven and serve immediately, garnished with fresh thyme if desired. Enjoy these hearty, flavorful sandwiches hot from the oven!

Tips for Perfect French Onion Veggie Subs

1. Caramelizing the Onions: Caramelizing onions can take some time, but it’s well worth the effort. If you’re short on time, you can speed up the process by using a medium-high heat, but keep in mind that the onions may not become as sweet or tender as when cooked slowly over low heat.
2. Customize the Veggies: While this recipe calls for bell peppers, zucchini, and mushrooms, feel free to add any vegetables you enjoy. Roasted eggplant, spinach, or even roasted tomatoes would work beautifully in this sub.
3. Cheese Options: While Swiss and Gruyère cheeses are traditional for French onion soup, you can experiment with other cheeses like cheddar or gouda for a different flavor. The key is to use a cheese that melts well.
4. Broil for Perfect Melt: To get the cheese perfectly melted and bubbly, broil the subs for just a minute or two. Keep a close eye on them as the broiler can work quickly.
5. Make-Ahead Tips: The caramelized onions and sautéed veggies can be made in advance and stored in the fridge for up to 3 days. This makes assembling the subs even quicker when you’re ready to eat.
6. Use Crusty Bread: A crusty baguette or sub roll is key to creating the perfect veggie sub. It adds texture and holds up well to the juicy onions and melted cheese.
7. Add Extra Toppings: Feel free to add extras like avocado, arugula, or even a fried egg to take the veggie sub to the next level.