Cook the zucchini
Heat ¼ cup of olive oil in a large heavy-bottomed pot or Dutch oven over medium-high heat.
Add the zucchini and season with 1 teaspoon salt and ½ teaspoon black pepper.
Cook the zucchini, stirring occasionally, until it expels liquid, the liquid cooks off, and the zucchini caramelizes into a jam-like, spreadable consistency, 10 to 12 minutes. If you start to notice any browning at the bottom of your pot, reduce the heat to medium.
Once jammy, transfer the zucchini into a medium bowl and set it aside.
Cook the pasta
In the same pot (don’t worry about wiping off any browned bits or pieces of zucchini that might be left in the pot), add 3 ¼ cups water and bring it to a boil over high heat. Season the water with the remaining 1 ½ teaspoons salt. Once the water is boiling, add the pasta and cream cheese, and reduce the heat to medium-high. Break up the cream cheese with the back of a wooden spoon to disperse throughout. It’s okay if the pasta isn’t completely submerged in liquid. Cook, stirring frequently until the pasta is al dente and liquid is reduced and creamy, 11 to 13 minutes. If all the moisture cooks off and the pasta is still undercooked, add a splash of water.
Combine and serve
Add the cooked zucchini, lemon zest, and lemon juice and cook until warmed through, 2 minutes.
Add a splash of water to create a thin, glossy sauce, if needed.
Season to taste with salt and pepper, if needed.
Divide between bowls and top with toasted walnuts. Serve.
