Place ½ cup of the toasted walnuts in a food processor. Puree until finely chopped. Add the ricotta and pulse until smooth. Set aside.
Bring a large pot of salted water to a boil. Cook the pasta 1 minutes less than package instructions or until not quiet al dente, about 9 minutes. Drain, reserving 1 ½ cups of pasta water.
In a large skillet combine the olive oil with the ricotta walnut mix, salt, and 1 cup of pasta water. Place over medium heat and bring to a simmer. Add the cooked pasta, and dust with the parmesan, and lemon zest. Toss well to coat. Add the lemon juice and peas and simmer for another 2 minutes or until the pasta is al dente and the sauce is coating the pasta. Add more pasta water as needed along the way to maintain a sauce consistency. Roughly chop the remaining walnuts and sprinkle over the top before serving.
