Preheat oven to 350º. Lightly grease (using oil of choice) a 9-inch round pie pan, set aside.
In a medium saucepan, saute shrooms, onions, and garlic for 3-5 minutes until they begin to soften. Add broth, frozen veggies, and nutritional yeast- bring to a boil. Slowly pour in almond milk/cornstarch mixture, stirring constantly until thickened. Season with pink salt and pepper, stir in parsley, and then remove from heat.
Meanwhile, in a stand mixer (or with electric beaters), cream together cooked sweet potatoes, almond milk, vegan cheese, and nutritional yeast. Season with pink salt and pepper.
Transfer shroom and veg mixture to pie pan, and distribute evenly with a spoon. Top with cheesy sweet potato mixture, and carefully pull to the edges. Top with additional vegan cheddar, if desired.
Bake for 15-20 minutes, or until the cheese is melted and/or slightly browned. Top with parsley garnish, if using.