Combine the first 6 ingredients in a small bowl, and set cornstarch mixture aside.
Heat 1 tablespoon oil in a stir-fry pan or a wok over medium heat. Add minced ginger and crushed garlic; stir-fry 30 seconds. Add sliced mushrooms, asparagus, and leek; stir-fry for 3 minutes. Add the cubed tofu; stir-fry 4 minutes. Stir in cornstarch mixture. Bring to a boil; cook for 1 minute.