Preheat oven to 375°F. Grease an 8- or 9-inch pie pan, or 8 ramekins with cooking spray.

Heat evoo in a large sauté pan on medium. Sauté leek for 1 minute, or until it softens. Add mushrooms and sauté for 2 to 3 minutes more. Add chopped beet greens, and cook until wilted. Remove from heat and set aside.

In a small pot, heat vegan butter over medium heat. Whisk in flour, and cook for 1 minute. Add almond milk a little at a time, whisking it to form a smooth mixture with each addition. Bring to a gentle simmer, and cook for 5 to 7 minutes while stirring continuously. Season sauce nutmeg, salt, and pepper.

Stir almond milk mixture into greens. Pour mixture into prepared pan or pans. Top with bread crumbs or cracker crumbs, spray tops with cooking spray.

Bake at 375°F for 45 minutes, or until golden brown on top. Remove from oven a cool slightly before serving.