Bring a medium saucepan filled with salted water to a boil. Add the fussilli and cook until very al dente, about 5-7 minutes. Drain the pasta and set it aside.
To the same (empty) saucepan (no need to clean it out), set over medium heat, combine the water, chicken broth and lemon juice. Bring the broth mixture to a simmer. Salt and pepper the broth to taste. I used very low-sodium broth so I had to add a pretty generous amount. Also, take note that Parmesan is salty so keep that in mind.
Turn the heat to low. Just a heads up: the next few steps go very quickly so be sure to get ready. Mix in the finely grated Parmesan. Next, create whirlpool with a spoon in the broth. In one slow and steady stream, pour in the beaten egg. Mix in the fresh baby spinach and give it a good mix. You should see the eggs in little cooked bits. Add the reserved fussili pasta. Give it one last taste and adjust the salt according to taste.
Divide amongst bowls. Garnish each serving with more black pepper and additional strips of Parmesan.