Heat the butter in a large, 12-inch skillet over medium-high heat.
When melted and foamy, add the zucchini noodles. Cook, stirring often, until just tender, about 4-5 minutes.
Add the garlic and cook, stirring, for 1 more minute. Turn the heat off.
Mix in the kosher salt, black pepper, red pepper flakes, and parmesan.
Serve immediately.
Video
Notes
Overcooking the zucchini strands will result in them being soggy. It's much like cooking pasta al dente. You want the strands to still have a "bite." You don't want them to be too soft. So ensure you don't cook them longer than necessary in the first step before adding the garlic. Then, after adding the garlic and letting it cook briefly, turn the heat off immediately.
You can keep the leftovers in the fridge, in an airtight container, for up to four days. Reheat them gently, covered, in the microwave at 50% power. If you like cold leftover pasta, you'll enjoy eating these leftovers cold. I certainly do!