FOR each serving: Heat 1 tsp. oil on griddle on medium heat. Spoon 1/2 cup hash browns into a mound onto griddle; press lightly to form circular cake. Cook until evenly browned on both sides, turning once. Season with salt and pepper. Transfer to serving plate; cover to keep warm.
ADD 1 tsp. oil and 3 oz. eggs to griddle; cook until eggs are done, keeping in large pieces. Spoon onto potato pancake.
HEAT 1 tsp. oil on griddle. Add 1/3 cup each mushrooms, steak and spinach, 2 Tbsp. each onions and tomatoes, and 1/4 tsp. parsley; cook until heated through, stirring frequently. Spoon over eggs. Drizzle with 1 Tbsp. steak sauce; top with 2 Tbsp. cheese.