Bring a large pot of water to a boil. Salt it generously, it should taste like mild seawater. Cook the pasta according to package directions until al dente. Before you drain it, scoop out at least 1 cup of pasta water and set it aside. Drain the pasta and set it aside.

While the water is coming to a boil, toast the walnuts. Place them in a small dry skillet over medium heat. Shake the pan every 30 seconds or so and cook for 3 to 4 minutes, until they smell nutty and look lightly golden. Pour them onto a cutting board right away so they stop cooking, then roughly chop them. Set aside.

Heat 2 tablespoons of the olive oil in a large skillet over medium-high heat. When the oil shimmers, add the zucchini in a single layer. You may need to do this in two batches if your skillet is crowded. Let the zucchini sit without stirring for 2 to 3 minutes so it develops some golden color on the bottom. Flip and cook another 2 minutes. Season with the salt and pepper.

Reduce the heat to medium and push the zucchini to the edges of the pan. Add the remaining 1 tablespoon of olive oil to the center of the skillet, then add the garlic. Cook the garlic for about 60 seconds, stirring it, until fragrant and just starting to turn golden at the edges. Stir it into the zucchini.

Add the drained pasta to the skillet. Pour in 1/3 cup of the reserved pasta water and scatter the goat cheese over the top. Toss everything together over medium-low heat, letting the cheese melt into a loose, creamy coating. Add more pasta water a splash at a time if it looks dry. You want a saucy consistency that clings to the pasta without pooling in the pan.

Taste and adjust the salt and pepper. Stir in the lemon zest if using. Divide into bowls, then top each portion with the toasted walnuts and a pinch of fresh thyme. Serve immediately.