Italian Burgers Recipe – Sunset Magazine

Ingredients

• 4 slices red onion, about 1/4 in. thick
• 2 tablespoons balsamic vinegar
• 1/4 cup olive oil, divided
• 3/4 cup chopped giardiniera*
• 1/3 cup mayonnaise
• 1 tablespoon chopped fresh oregano leaves
• 1 1/2 pounds ground lean beef
• 1 teaspoon kosher salt
• 1/2 teaspoon pepper
• 4 ciabatta or focaccia buns, split
• 4 slices provolone cheese
• About 2 cups lightly packed arugula