Steak and Avocado Sandwiches

Ingredients

• 1 pound flank steak
• 3 tablespoons soy sauce
• 1 teaspoon dijon mustard
• 3 garlic cloves finely chopped or pressed
• 1 teaspoon dried rosemary
• 1/2 teaspoon black pepper
• 1 teaspoon kosher or sea salt or to taste, divided
• 2 tablespoons olive oil
• 4 teleras, bolillos, or small baguettes
• 1 can La Costeña refried black beans
• 1 ½ cups or 6 ounces ounces shredded melty cheese as Oaxaca, Monterey jack, Muenster
• 2 ripe avocados, pit removed, diced
• 2 scallions rinsed, tops removed, white and light green parts thinly sliced
• 3 tablespoons coarsely chopped cilantro leaves
• 1 fresh jalapeño or serrano chile more or less to taste, finely chopped
• Juice of 1 lime
• 1 can La Costeña sliced pickled jalapeños