- 1 (3 1/2- to 4-lb) spaghetti squash
- 1/4 cup walnuts (3/4 oz)
- 1/2 garlic clove
- 1 1/3 cups packed fresh flat-leaf parsley
- 3 tablespoons extra-virgin olive oil
- 2 1/2 tablespoons finely grated Pecorino
- 1 tablespoon water
- 1 teaspoon salt
- 1/4 teaspoon black pepper
- 1/4 teaspoon finely grated fresh lemon zest
- Pierce squash all over with a sharp small knife. Cook in a microwave oven (see cooks' note, below) at high power (100 percent) 8 minutes, then turn over and microwave until squash gives when pressed gently, 8 to 10 minutes more. Cool squash 5 minutes.
- While squash is cooking, toast nuts in a dry small heavy skillet over moderate heat, stirring frequently, until fragrant and a shade darker, about 6 minutes, then cool completely.
- Pulse nuts and garlic in a food processor until finely ground. Add parsley, oil, cheese, water, salt, pepper, and zest and pulse until parsley is coarsely chopped.
- While squash is still hot, cut off stem from squash and discard, then carefully halve squash lengthwise (it will emit steam) and discard seeds. Working over a bowl, scrape out squash flesh with a fork, loosening and separating strands. Toss with pesto in a bowl.