In a large pot or deep skillet, combine the dry spaghetti, vegetable broth, water, minced garlic, salt, black pepper, red pepper flakes, and olive oil.
Bring the mixture to a boil over medium-high heat, stirring occasionally to prevent the pasta from sticking.
Once boiling, reduce the heat to medium and continue to cook, stirring frequently, until the pasta is al dente and most of the liquid has been absorbed, about 10 to 12 minutes.
Add the chopped spinach to the pot and stir until wilted, about 1 to 2 minutes.
Reduce the heat to low and stir in the heavy cream, grated Parmesan cheese, lemon zest, and lemon juice until well combined and creamy.
Cook for an additional 2 minutes, stirring gently to combine all flavors.
Remove from heat and sprinkle with fresh parsley before serving.