Here’s the step‑by‑step process, rephrased and polished:

1. Start by cooking your pasta until al dente, following the directions on the package. Be sure to reserve at least one cup of pasta water before draining.

2. As the pasta cooks, set your oven to preheat at 375°F (190°C).

3. In a baking or casserole dish, combine the sliced zucchini, garlic cloves, pine nuts (or walnuts), and chopped onion. Add a drizzle of olive oil and stir gently to ensure everything is evenly coated.

4. Roast for about 25 minutes, or until the zucchini is just beginning to turn golden and the garlic and onion are softened and fragrant. Remove from the oven and let cool for a few minutes.

5. Move the roasted zucchini, nuts, garlic, and onions into a high-powered blender.

6. Include the basil, nutritional yeast, lemon juice, olive oil, salt, and pepper in the blender. Blend until you achieve a smooth yet slightly textured consistency that resembles classic pesto.

7. In a large skillet over low heat, combine the cooked pasta with the zucchini pesto and toss to coat.

8. Gradually pour in the reserved pasta water, stirring until the sauce reaches your desired thickness.

9. Serve warm, optionally finishing with vegan Parmesan or extra nutritional yeast for a cheesy flair.