Start by preparing your vegetables. Dice the onion, chop the bell pepper, and slice the mushrooms. Be sure to wash the heirloom tomato and cut it into thick slices. Clean those romaine leaves as well.

In a large skillet, heat the olive oil and butter over medium heat. Toss in the diced onion first, allowing it to soften for about two minutes.

Once it starts to become translucent, add in the bell pepper and mushrooms. Cook them for an additional five minutes until they’re tender and lightly browned. The aroma will fill the kitchen. Your nose will thank you!

As the veggies cook, preheat your oven or a toaster oven to about 350°F (175°C). Slice your sesame seed buns in half and place them on a baking sheet. When the oven is ready, toast the buns for about 5 minutes or until they’re golden brown.

Now it’s time to assemble! Take the toasted buns and spread a generous amount of mayonnaise on the bottom half. Layer on the sautéed veggies right off the skillet.

Stack those slices of cheddar cheese on top of the veggies. Then, add your slices of heirloom tomato and the romaine leaves. Finally, drizzle ketchup and a touch of Dijon mustard over everything. Finish with the top bun.

Slice the sandwich in half for easy handling. Serve it immediately while everything is warm. Add those crispy fries to the plate, and there you have it. A beautiful Five Guys-inspired Veggie Sandwich.