Bring a large pot of generously salted water to a boil. It should taste like the sea — that's your only chance to season the pasta from the inside out.
Cook the pasta: Drop the spaghetti into the boiling water and cook it for 2 minutes less than the package directions say. It will finish cooking in the sauce.
Make the zucchini ribbons: While the pasta cooks, use a Y-peeler to turn the zucchini into long, thin ribbons. Stop when you hit the seedy core.
Blister the tomatoes: In your 12-inch skillet, heat the olive oil over medium-high heat. Add the cherry tomatoes in a single layer. Let them cook undisturbed for about 2 minutes until deeply blistered. Smash a few with the back of a spoon to release their juices.
Add the aromatics: Toss in the sliced garlic and red pepper flakes. Cook for 30 seconds, stirring constantly, until fragrant and just starting to turn golden.
Create the sauce base: Ladle about 1/2 cup of the pasta water into the skillet. Let it simmer for a minute, scraping up any browned bits. The liquid will reduce and thicken into a silky sauce.
Combine everything: Using tongs, transfer the undercooked spaghetti directly from the pot into the skillet. Do not drain — the residual water adds starch. Add the zucchini ribbons on top.
Toss and finish: Toss everything together for 1 to 2 minutes over medium heat, until the pasta is al dente and the zucchini has softened slightly. If dry, add another splash of pasta water.
Serve immediately: Turn off the heat. Add the torn basil and toss once more. Divide among bowls and shower generously with Parmesan. Twirl the pasta high in the center of the bowl.