The flavors in this colorful stir-fry are a fantastic combination of savory, sweet, tangy, garlicky, spicy and nutty. Briefly marinating the sliced tenderloin means that the meat browns beautifully in the skillet and also adds flavor and moisture to an otherwise lean and mild cut. Balsamic vinegar may seem like an odd ingredient in a stir-fry, but it mimics the subtle sweetness, moderate acidity and maltiness of Chinese black vinegar and probably already is in your pantry. Serve with steamed white rice.