Naan Round Steak Sandwich – Stonefire Authentic Flatbreads

Ingredients

• 8 Stonefire® Caramelized Onion Naan Rounds
• ¼ cup water
• ¼ cup cider vinegar
• 2 Tbsp sugar
• 1 cup thinly sliced red onion
• 1 pound flank steak, trimmed
• 1 ½ tsp olive oil
• ¼ tsp kosher salt
• ¼ tsp freshly ground black pepper
• 2 Tbsp grainy French mustard
• 4 green leaf lettuce leaves