The name says it all. Who wouldn't want a grilled steak sandwich with homemade caramelized onions, balsamic vinegar, goat cheese, and mushrooms?!

Steak Sandwiches with Balsamic Onions and Mushrooms

Melt 2 tablespoons butter in a large nonstick skillet over medium heat. Add onions; sprinkle with brown sugar and 1/8 teaspoon each of salt and black pepper. Cook over medium-low heat for 25 to 30 minutes or until golden and starting to caramelize, stirring occasionally. Toss with 1/2 teaspoon balsamic glaze. Set onions aside.

Meanwhile, melt remaining 1-1/2 tablespoons butter in a medium nonstick skillet over medium heat. Add mushrooms. Cook over medium-low heat for 10 to 12 minutes or until golden, stirring occasionally. Set mushrooms aside.

Pat steaks dry with paper towels. Rub both sides of steaks with olive oil. Sprinkle and rub with remaining 1/2 teaspoon each of salt and black pepper. Let steaks stand at room temperature for 20 minutes. Meanwhile, preheat a charcoal or gas grill for direct cooking over medium heat. 

Grill steaks for 8 to 12 minutes or until medium-rare doneness (130 degrees), turning halfway through. Transfer steaks to a clean cutting board. Loosely cover with foil; let rest for 5 minutes.

To assemble sandwiches, divide goat cheese among 4 bread slices. Thinly slice steaks across the grain. Place steak slices on goat cheese; top with onions, mushrooms, roasted red peppers, and arugula. Drizzle with balsamic glaze. Place remaining 4 bread slices on top.