- Preheat the oven to 400°F . Lightly spray an 8-inch square or 10-inch round baking dish with olive oil. Alternatively, if you have a shallow Dutch oven or large cast-iron skillet, you can use that to cook the filling, then bake the casserole.
- To make the topping : Place the sweet potatoes in a medium pot and cover with water. Bring to a boil and cook for 8 to 10 minutes, until easily pierced with a fork. Remove from the heat and drain.
- Add the milk, olive oil, nutritional yeast (if using), and garlic powder and mash until smooth. Alternatively, you can use a hand mixer or food processor. Once smooth, add salt and pepper.
- While the sweet potatoes are boiling, make the filling : Heat the olive oil in a large, shallow saucepan that can go into the oven (or a Dutch oven or cast-iron skillet) over medium heat. Add the onion and garlic and sauté for 2 to 3 minutes, until the oni
- Add the carrots and celery and cook for another 3 minutes. Add the beans, mushrooms, rosemary, and thyme. Cook for about 5 minutes, stirring occasionally.
- Combine the broth, liquid aminos, and tomato paste in a cup or small bowl and stir until combined. Add to the vegetables with the sun-dried tomatoes and olives and cook for about 5 minutes more. Remove from the heat and add the lemon juice, salt, and peppe
- Pour the filling into the prepared pan (or leave it in the Dutch oven). Spread the mashed sweet potato over the top. Sprinkle with the Pepita Parmesan and rosemary.
- Bake for about 15 minutes, until the top is crispy and golden. Serve immediately. Leftovers will keep in an airtight container in the fridge for up to 4 days.