In a mixing bowl, combine all-purpose flour, baking soda, and salt. Drizzle in canola oil and mix until it resembles coarse breadcrumbs. Gradually add boiling water to form a shaggy dough, then roll out.

Transfer to a pie dish, crimp edges, and set aside.

Wrap tofu in paper towels and press with a heavy object for 15-20 minutes.

Blend pressed tofu, nutritional yeast, melted margarine, salt, and black pepper until creamy. Gradually pour in soy milk.

Heat olive oil in a skillet, add diced onion and sauté until translucent. Add mushrooms and a pinch of salt, cook until browned. Add spinach and cook until wilted.

In a bowl, combine cooled vegetables, tofu custard, vegan cheese, and vegan bacon bits. Stir until well incorporated.

Preheat oven to 400°F (200°C). Pour filling into crust and optionally brush with melted margarine. Bake for 50-60 minutes until set and golden.

Let the quiche cool on a wire rack for at least 15 minutes before slicing. Serve warm or at room temperature.