In a Dutch oven or large pot, add in the spaghetti, navy beans, water, olive oil, and salt. Bring the pot to a boil over medium-high heat.
While boiling, be sure to turn the pasta frequently with tongs, for 5 minutes so everything is sticking together.
Next, add in the spinach and shrimp. and cook until pasta is al dente and most of the liquid has evaporated.
Add in the lemon juice, lemon zest, butter, and parmesan, and mix everything together. The butter will melt and coat the noodles, making them silky!
Top off with some red pepper flakes and serve warm.