In a large pot or deep skillet, heat olive oil over medium heat.
Add the chopped onion and sauté for 3-4 minutes until translucent.
Add the minced garlic and cook for 1 minute until fragrant.
Add the sliced zucchini to the pot and cook for 3 minutes, stirring occasionally.
Pour in the vegetable broth and water, then add the dried spaghetti pasta.
Add salt, black pepper, and red pepper flakes, then stir to combine.
Bring the mixture to a boil, then reduce heat to medium-low and simmer, stirring occasionally, until the pasta is cooked al dente and most of the liquid is absorbed, about 10-12 minutes.
Remove the pot from heat and stir in the grated Parmesan cheese until melted and well combined.
Sprinkle chopped fresh basil over the pasta before serving.