Portobello mushrooms have a meaty quality that makes them a healthy stand-in for the steak that you might expect to find in this kind of Chinese-style stir-fry. (But you can add some sliced steak, if you wish.) Broccolini is great for stir-frying because its thin stalks cook quickly. Don't confuse it with broccoli rabe, which it resembles -broccolini is much milder. This stir-fry also gets a non-Asian seasoning of thyme, which works beautifully with the other flavors.