Begin by heating sunflower oil in a heavy-bottom pot to 350°F. Slice zucchini into thin rounds, about 1/4 inch thick. Fry zucchini in small batches for 5-7 minutes until blistered and golden. Transfer to a plate lined with paper towels.

While zucchini is chilling, bring a large pot of salted water to a boil. Add spaghetti and cook according to package instructions until al dente, about 8-10 minutes. Reserve 1 cup of pasta water before draining.

In a large pan over medium-high heat, pour in olive oil. Once shimmering, add chilled zucchini and 2 ladles of reserved pasta water. Stir to combine and season with kosher salt and black pepper.

Add drained spaghetti to the pan with zucchini, tossing everything together until well coated. Remove from heat and mix in Parmesan cheese and butter, adding more pasta water if necessary to adjust consistency.

Plate the zucchini pasta, garnishing with additional Parmesan and fresh basil. Serve immediately while hot.