Melt butter in a large skillet.
Add minced garlic and cook until fragrant.
Add coarsely grated zucchini and cook until it releases all its water and turns to a soft, jam-like texture.
Cook spaghetti in heavily salted water until al dente, reserving a cup of pasta water.
Toss the cooked zucchini with the pasta, reserved pasta water, Parm, and basil.
Stir until a glossy zucchini sauce coats the pasta.
Serve in bowls with more Parm and basil.
