Heat up the cashew sauce in a pot (optionally, to reduce the baking time).
Spread half of the sliced potatoes and zucchini in the baking dish. Top evenly with half of the cashew sauce, then spread over the onions, garlic and mushrooms. Layer the rest of the potatoes and zucchini, then the rest of the mushrooms and sauce. (Make sure that the veggies are well covered with the sauce).
Bake the potato bake for about 50 minutes or until the potatoes are fork tender and soft. (If it gets too brown during baking, cover the dish with tin foil or baking paper. But note that the potatoes need more time to cook through when the dish is covered).
Optionally, sprinkle vegan cheese over a few minutes before done and continue baking until melted, about 5-10 minutes.
Garnish with chopped chives and toasted pine nuts or other toppings you like.