Heat a large flat-bottomed wok or a large skillet over high until hot (to test if it’s hot enough, flick a drop of water into the pan—it should evaporate immediately). Swirl in 1 tablespoon of the oil. Add the protein, and season with salt and pepper. Sauté, stirring occasionally, until lightly caramelized on the outside but still undercooked in the center, about 2 minutes. Transfer to a plate.
Swirl in another tablespoon of oil and add the hardy vegetables. Cook, stirring occasionally, until caramelized in spots, about 2-4 minutes.
Push the vegetables to one side of the wok. In the other side, add the remaining tablespoon of oil, followed by the garlic and ginger. Add the tender vegetables and toss everything together. Cook, stirring constantly, until crisp-tender, about 1-3 minutes.
Return the protein to the wok. Whisk the stir-fry sauce to distribute the cornstarch, and then add it as well. Cook, stirring gently, until the sauce comes to a boil coats the meat and vegetables, about 1 minute. Season to taste with salt and pepper. Serve the stir-fry over rice. Garnish with sliced scallions, if you’d like.