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1
Heat oven to 400 degrees F. Cook the pasta according to package directions.
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2
Reserve 1/2 cup of the cooking water, drain the pasta, and return it to the pot.
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3
Meanwhile, spread the walnuts on a rimmed baking sheet.
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4
Roast until fragrant, 5 to 6 minutes; transfer to a food processor and let cool.
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5
Heat 1 tablespoon oil in a large skillet over medium heat.
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6
Add the onion, season with 1/4 teaspoon each salt and pepper and cook, covered, stirring occasionally, until tender, 6 to 8 minutes.
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7
While the onions are cooking, using a vegetable peeler, remove 3 strips of zest from the lemon.
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8
Thinly slice the zest; add it to the food processor along with the garlic and pulse until finely chopped.
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9
Add the Parmesan, 1/4 cup peas, 2 tablespoons oil, and 1/2 teaspoon each salt and pepper and puree until smooth.
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10
Add the wine to the onions and simmer for 2 minutes.
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11
Add the remaining 1 cup peas and cook, tossing, until heated through.
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12
Toss the pasta with the walnut pesto (adding some of the reserved pasta water if the mixture seems dry).
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13
Add the onion mixture and toss to combine.
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14
Serve with a squeeze of lemon juice and additional Parmesan, if desired.
