Combine all ingredients, except potato and squash slices, in a bowl and mix well.
In a 9" cake pan, make a layer of potatoes, overlapping slightly. Follow with a layer of squash, overlapping slightly. Sprinkle with 2 tbsp of the nutritional yeast mixture. Repeat these layers until you reach the top of the cake pan.
Preheat oven to 400 degrees F.
Cover tart with foil and bake 30 minutes. Uncover and bake an additional 30 minutes.
Let cool 10-15 minutes before serving.