Ingredients

• 1 tablespoon vegetable oil
• 1 sweet onion (about 1 lb/500 g) sliced
• 1/4 teaspoon salt
• 1/4 teaspoon pepper
• 1/4 teaspoon granulated sugar
• 1/4 cup light mayonnaise
• 1 teaspoon chipotle sauce
• 4 buns cut in half
• 1 cup arugula leaf
• 1 cup romaine leaf

Marinated Flank Steak:

• 1/4 cup red wine
• 2 tablespoons canola oil
• 2 tablespoons vegetable oil
• 1 tablespoon balsamic vinegar
• 3 garlic cloves minced
• 1 tablespoon fresh rosemary minced
• 1 lb beef flank marinating steak
• 1/2 teaspoon salt
• 1/2 teaspoon pepper