Preheat your oven to 400°.
In an oven safe pan heat the olive oil over medium heat. Add the onions and reduce to medium low. Add the carrots and celery and allow to sautee for 15 minutes. Increase heat to medium and add the chunks of seitan and cook for about 5 minutes more, stirring occasionally to keep from sticking, but allowing to brown a bit. Stir in 2 T of flour and mix well to coat and distribute.
Pour wine over top of the seitan and veggies and use a wooden spoon to loosen up any brown bits. Add the veggie stock and stir well to continue breaking brown bits off the bottom. Add the rosemary, a few cracks of black pepper, and salt if you are using it (this is dependent on how salty your hash browns are). Allow to cook through for about 2 minutes, letting the sauce thicken up a little bit.
Remove from heat. Crumble the frozen hash browns in the bag (so they don't come out in one big chunk), then open and evenly distribute on top of the stew. Brush the hash browns with olive oil. Place in the oven and bake for 30 minutes. At that time, turn the broiler on and brown the top for up to 5 minutes, watching it the entire time. Don't burn your beautiful dinner!
Remove from oven, allow to cool for a minute, and serve!