Grind 1 tablespoon of the flaxseed with 1/4 cup water in a spice grinder until fairly smooth. Transfer to a small cup.

Repeat with remaining 1 tablespoon flaxseed and another 1/4 cup water. Alternatively, stir 2 tablespoons flaxseed meal into 1/2 cup water.

Preheat the oven to 375°F.

Line the bottom of a 10-inch round tart pan with a removable bottom with parchment paper.

In a food processor, pulse almond meal and half of the flaxseed mixture until dough begins to pull away from the sides of the bowl.

Gather into a ball and flatten into a disk. Press evenly into the bottom and up the sides of the prepared pan.

Bake until dried on bottom and barely golden on top edge, about 12 minutes. Cool completely on a rack.

Meanwhile, place delicata squash in a single layer on a parchment paper-lined baking sheet. Bake alongside crust until soft and browned on the edges, about 15 minutes.

Combine leek, mushrooms and 2 tablespoons water in a large skillet over medium heat. Cook, stirring frequently, until browned and softened, about 12 minutes.

Stir in garlic and soy sauce, and cook for 1 minute. Transfer to a medium bowl.

Stir in quinoa, butternut squash purée, sage, vinegar, pepper, 1 tablespoon of the yeast and remaining flaxseed mixture.

Scrape into tart crust and level top. Sprinkle with remaining 1 tablespoon yeast.

Arrange squash slices on top, pressing them lightly into filling.

Bake until browned and set, about 45 minutes. Cool for 15 minutes before serving.