To Make the Tortilla Pie:

1. Bring the water to a boil over high heat in a large saucepan and add the millet. Return the water to a boil, cover, and reduce the heat to medium. Cook for 20 minutes, or until the millet is very tender.
2. While the millet cooks, sauté the onion and poblano pepper over medium heat in a large saucepan until the onion turns translucent and starts to brown, about 8 minutes. Add water 1 to 2 tablespoons at a time to keep the vegetables from sticking. Add the garlic, cumin, basil, and oregano, and cook another minute.
3. Add the corn and tomato puree and remove the pan from the heat. Add the cooked millet, season with sea salt and black pepper to taste, and let cool.
4. When the millet is cool enough to handle, use a spatula to crumble it.
5. Preheat the oven to 425°F.
6. Place a layer of tortillas in the bottom of a 10-inch pie pan. Spread 1/2 cup refried beans over the tortillas and 1/2 cup salsa verde over the refried beans.
7. Sprinkle a third of the millet mixture over the salsa verde, and spoon a quarter of the cheese sauce over the millet mixture.
8. Add another layer of tortillas, 1/2 cup refried beans, 1/2 cup salsa verde, and another third of the millet mixture. Top the millet again with another quarter of the cheese sauce.
9. Repeat the process one more time with the tortillas, refried beans, salsa verde, millet mixture, and cheese sauce; add a final layer of tortillas; and then top with the remaining cheese sauce.
10. Bake for 20 to 25 minutes, until the top is lightly browned. Let cool 10 minutes before serving.
11. Serve garnished with the scallions and cilantro.

To Make the Cheese Sauce:

1. Combine the potato, bell pepper, onion, and cashews in a small saucepan and cover with water.
2. Bring the water to a boil over high heat, reduce the heat to medium, and cook until the potatoes are very tender, about 10 minutes. Drain the vegetables, reserving 3/4 cup of the cooking water.
3. Combine the potato mixture, reserved cooking water, tahini, lemon juice, nutritional yeast, arrowroot powder, and sea salt in a blender. Process on high until everything is smooth and creamy, about 3 minutes. Store the sauce in an airtight container in the refrigerator for up to 5 days.