PREHEAT oven to 400°F. Lightly grease a pie dish with olive oil.
PREP your veggies, using a mandolin slicer for the potatoes if you have one. Otherwise, a sharp chef’s or Santokku knife will do the trick.
MAKE the crust: Toss potato slices with olive oil, salt, and pepper. Spread the potato slices out on the bottom and sides of the pie dish, slightly overlapping the slices as needed to fit in the dish.
BAKE the crust for 15 minutes until the potatoes are tender but not brown. Remove from oven and turn the heat down to 350°F when done.
MEANWHILE, cook the veggies: Heat olive oil in a skillet over medium heat. Add onion and some of the salt and cook until onions start to brown, stirring occasionally, for about 3 minutes.
ADD garlic, mushrooms, zucchini, and remaining salt. Cook, stirring occasionally, until mushrooms and zucchini are just tender, for about 5 minutes.
STIR in spinach and cook another 30-60 seconds until spinach wilts.
REMOVE from heat and let the veggies cool for a bit while you prepare the tofu filling.
TO MAKE the tofu filling, add all ingredients to a food processor and blend until smooth. You can add an extra tablespoon of soy milk if needed to help blend.
MIX the veggies with the tofu filling. Spread the filling out over the potato crust. Use a spatula or spoon to smooth out the top.
BAKE at 350°F for 30 minutes, until golden on top and the filling is firm. Cool for 10-15 minutes before slicing.