Preheat oven to 375°F.

Bake pie crust for 10 minutes until lightly golden brown. Remove from oven and set aside.

Place a large sauté pan over medium heat. Once pan is hot, add olive oil, onions and salt and cook for 20 minutes, stirring occasionally. Add spinach and sauté 5 minutes more, making sure to combine onions and spinach.

In a medium mixing bowl, whisk eggs, teriyaki marinade and sauce and soy milk until frothy. Add onion-spinach mixture to egg mixture, stir to combine, then pour into par-baked pie crust. Bake at 375°F for 35 minutes until puffed and golden brown on top.

Allow to cool before slicing. Serve warm or room temperature.

Store quiche, covered in the fridge for up to 48 hours or freeze for up to a month.