Whisk together vinegar, oil, and sugar in a bowl. Reserve 1/4 cup mixture; transfer remaining marinade to a resealable plastic bag. Season lamb with salt and pepper and add to bag, turning to coat. Let marinate in refrigerator, turning occasionally, at least 1 hour and up to 4 hours.
Let chops stand at room temperature 30 minutes. Heat a large skillet over medium heat. Working in batches, remove lamb from marinade and add to pan. Cook, flipping once, until an instant-read thermometer inserted in thickest part (avoiding bone) registers 125 degrees, about 8 minutes. Transfer to a plate and let stand 10 minutes.
Whisk reserved marinade to combine. Divide arugula, fruit, pepitas, and mint among plates. Season with salt and pepper; drizzle with reserved marinade. Top with lamb; serve immediately.