In a large skillet, cook beef and onion over medium heat until meat is no longer pink, crumbling beef; drain. Add the potatoes, water, salt and pepper. Cover and simmer until potatoes are tender, about 20 minutes. , Add tomatoes; cook for 5 minutes. Pour eggs over mixture. Cook and stir until eggs are completely set. Top with cheese. Cover and cook until cheese is melted, about 1 minute.