Chef John's Ultimate Steak Sandwich

Details

Ingredients

• 1 (2 pound) fully-trimmed flat iron steak
• salt and pepper
• 8 ounces brown clamshell mushrooms, grilled, separated
• salt and pepper to taste
• 1 tablespoon sherry vinegar
• 2 tablespoons extra virgin olive oil
• 3 tablespoons barbeque sauce
• 2 tablespoons vegetable oil
• 1 tablespoon cider vinegar
• 6 hot dog buns
• ½ cup mayonnaise, or as needed
• 1 cup arugula leaves, or as needed
• 1 cup quartered cherry tomatoes