In small bowl mix together salt, pepper.soy sauce and check if it is to your liking. Add the beef in it and mix to coat. Marinate for and hour.
Heat skillet in medium heat with oil and pour beaten eggs. Cook and stir until eggs are thickened and no liquid egg remains; remove from heat. Set aside.
Add oil in the same skillet and saute' sliced mushroom and season with salt and pepper. Transfer to a small bowl and drain excess liquid. Set aside.
Heat the skillet again and add in oil. Cook the beef until no longer pink. Season accordingly and remove from the pan. Drain excess oil and let cool.