Preheat oven to 350°F. Lightly grease a 9×13-inch baking dish.

Spread the 20 ounces frozen shredded hash browns evenly in the prepared dish and let them thaw for about 15 minutes. After thawing, press the hash browns into an even layer.

Heat a large skillet over medium heat. Crumble and cook the 1 pound vegan sausage until browned, about 5–8 minutes.

Add the 1 small diced onion, 1/2 red bell pepper (diced), and 1/2 green bell pepper (diced) to the skillet with the sausage and cook until the vegetables are softened, about 3–5 minutes. Remove the skillet from the heat and let the mixture cool slightly.

Spread the cooked sausage and vegetable mixture evenly over the hash brown layer in the baking dish.

Evenly sprinkle the following over the sausage-vegetable layer: 1/2 teaspoon Italian seasoning, 1/2 teaspoon garlic powder, 1/2 teaspoon onion powder, 1/4 teaspoon paprika. Then sprinkle 1 1/2 cups shredded vegan cheddar cheese over the top.

In a medium bowl, whisk together the 2 (16-ounce) containers vegan egg substitute, 4 1/2 tablespoons all-purpose flour, 1/2 teaspoon baking powder, and kosher salt to taste until the mixture is smooth and no lumps remain.

Pour the egg mixture evenly over the assembled ingredients in the baking dish.

Bake uncovered in the preheated oven for 55–60 minutes, or until the center is set and firm (a knife or toothpick inserted near the center should come out mostly clean). If the top is browning too quickly, loosely tent with foil for the last 10–15 minutes.

Remove the casserole from the oven and let it rest for 5 minutes. Garnish with chopped fresh parsley or chopped green onions, slice, and serve.