Perfect Salmon Burgers

INGREDIENTS

• 2 scallions, chopped
• 1 cup plus 2 tablespoons panko (Japanese breadcrumbs)
• 2 tablespoons dijon mustard
• 1 tablespoon lemon juice
• Kosher salt and freshly ground black pepper
• 1 1/4 pounds center-cut salmon fillet, skin and pin bones removed
• 1 tablespoon mayonnaise
• Pinch of cayenne pepper
• 1/2 teaspoon grated lemon zest
• 2 tablespoons extra-virgin olive oil, plus more for brushing 4 brioche buns, split
• Tartar sauce and arugula, for topping