Spicy Steak and Parmesan Sandwiches / Jill Silverman Hough

Ingredients

• 1 1/4 pounds flank steak, about 1 inch thick
• 1 teaspoon coarse kosher salt, or more to taste
• 1/2 teaspoon freshly ground black pepper, or more to taste
• 1/2 cup grated Parmesan cheese
• 1/3 cup mayonnaise
• 1/4 cup prepared horseradish
• 2 cloves garlic, pressed through a garlic press or minced
• 1/2 teaspoon cayenne pepper
• 4 sandwich rolls or 1 baguette cut into 4 pieces, split
• 1/2 small red onion, thinly sliced
• 4 cups spring mix greens (about 2 ounces)