Bacon and Egg Sandwiches with Pickled Spring Onions

INGREDIENTS

• 4 spring onions or 6 scallions, whites only, thinly sliced
• 1/4 apple cider vinegar
• 2 sugar
• 1 kosher salt
• 12 slices thick-cut bacon
• 2 pure maple syrup
• 1/4 mayonnaise
• 1 Sriracha
• 8 slices white sandwich bread, such as Pullman
• 2 unsalted butter
• 4 large eggs
• Kosher salt, ground pepper
• 1 arugula leaves