Heat up cast iron skillet over medium-high heat. Once skillet is hot, add 1 T oil and 2 tablespoon plant based sausage. Chop up sausage with spatula, and cook until browned and warm. Remove from skillet.
Add 1 T oil, swirl around pan. Sprinkle 1 cup of frozen hashbrowns on pan, then top with ¼ teaspoon salt. Spread out. Cook for 3-4 minutes, or until bottom starts to brown. While hashbrowns are cooking, dice ~¼ medium sized onion, and slice 3-5 mushrooms by cutting them in half, from top to stem and then placing flat sides down and slicing thinly from top of mushroom to stem.
Flip hashbrowns and cook for another 3-4 minutes. Remove from heat once browned.
Add in another 1 T oil, diced onions, sliced mushrooms, and remaining salt. Spread out vegetables so they're all touching the bottom of the pan. Cook for about 5 minutes, until softened and onions are translucent. Stir occasionally.
Add hashbrowns, 'sausage', and ¼ c diced green peppers back into pan, stir together and remove when everything is hot, about 3-4 minutes. Sprinkle with cheese if desired and serve immediately.
Optional: garnish with fresh parsley, serve with hot sauce.