Chilean Steak Sandwich

Name: Chilean Steak Sandwich
Cuisine: American, Latin American
Ingredients: 4 large sandwich rolls (Marraqueta or French rolls); 500g (1.1 lb) thinly sliced beef steak (sirloin or tenderloin); 1 tbsp vegetable oil; Salt and freshly ground black pepper (to taste); 2 cups cooked green beans (trimmed and halved); 2 medium ripe tomatoes, thinly sliced; 4 tbsp mayonnaise; 1 tsp ají verde or mild chili pepper (optional); 1 cup iceberg lettuce (optional, for added crunch)