Heat the olive oil and garlic in a large sautee skillet. Add the sweet potato and mushrooms and a splash of water, cook until the sweet potato noodles are soft. Time varies according to thickness of noodle, fork test after 6-8 minutes.
Meanwhile, whisk together the sauce ingredients.
In a small bowl, whisk together the cornstarch and water. Set aside.
Add the spinach and sauce to the noodles. Toss to coat. Let cook for a few minutes and then stir in the cornstarch mixture. Let cook until the spinach is wilted and the sauce is thickened.