In a large skillet, cook bacon over medium-high until fat is rendered and bacon is crisp, 8 minutes. Transfer to paper towels to drain. Meanwhile, in a small bowl, stir together yogurt and Parmesan; season with salt. Spread yogurt mixture over half of each lavash piece. Spread mustard on other half. Layer steak, bacon, onion, and arugula on each lavash piece and roll up. Cut each roll into four pieces.