Trim zucchini ends and cut into a mix of sizes and shapes such as rounds, half-moons, and chunks. Heat olive oil in a deep skillet over medium-low. Add garlic cloves and one piece of zucchini to the pan.
Once the zucchini is bubbling, you’re ready to start frying the rest in batches (don’t overcrowd the pan). Remove and discard the garlic cloves before they get burnt (this process flavors the oil).
Add zucchini in small batches. As pieces begin to soften, transfer them to a bowl and keep adding more raw zucchini to the pan. Maintain a mix of doneness for texture, removing some slightly undercooked pieces to finish steaming in the bowl.
Meanwhile, cook spaghetti in boiling salted water to al dente. Reserve 1 cup pasta water.
Transfer a portion of the cooked zucchini (I like using the mushier pieces) to another bowl and blend with an immersion blender (or mash by hand), until mostly blended but not a full puree.
Return blended zucchini back to the skillet with leftover oil over low heat. Toss to cook briefly, then add in the rest of the fried zucchini.
Using tongs, transfer al dente spaghetti directly to the skillet along with torn basil leaves, and a ladle of pasta water. Toss to combine everything together.
Turn off the heat and add 1 cup pecorino with another splash more of pasta water. Toss vigorously to create a creamy, emulsified sauce. Taste then add more salt and freshly cracked black pepper, if needed.
Serve with more pecorino, fresh basil, and black pepper if desired.