Heat the neutral oil in a large pot over medium heat.
Add the chopped onion and garlic; sauté until softened and fragrant, about 5 minutes.
Add the chopped zucchini, red pepper flakes, and a pinch of salt; cook for another 5 minutes, stirring occasionally.
Pour in the vegetable broth and bring the mixture to a boil.
Reduce heat and simmer for 15 minutes, until zucchini is tender.
Remove the pot from heat; add basil leaves.
Use an immersion blender to puree the soup until smooth and velvety.
Season with salt and pepper to taste.
Drizzle with extra-virgin olive oil if desired before serving.