Mabel's Steak Sammies | Recipe Reader

Ingredients

• 1/2 small red onion, thinly sliced
• 3 tablespoons fresh lemon juice, divided
• kosher salt, to taste
• black pepper, to taste
• 2 tablespoons balsamic vinegar
• 2 tablespoons whole-grain mustard
• 1/2 tablespoon Dijon mustard
• 1 (1.25-1.50-pound) hanger steak, can substitute flank or skirt steak, fat trimmed
• 4 small ciabatta rolls, split
• 1 bunch fresh arugula, thick stems discarded
• 1 tablespoon olive oil
• 1 ounce parmesan cheese, shaved