Place half of the toasted walnuts in a mini food processor and pulse until finely chopped. Add the ricotta and pulse again until smooth and set aside.
Bring a small pot of salted water to boil and cook the fusilli until just under al dente, following package instructions. Reserve 3/8 cup (90 ml) of pasta water, then drain.
In a medium sized skillet, add olive oil, garlic and thyme and sauté on medium heat for 1 minute or until garlic and thyme are fragrant.
Add the walnut and ricotta mixture, salt and 3/4 of the pasta water and bring to a simmer to heat through.
Add cooked pasta, Parmesan cheese, and lemon zest and toss well to coat.
Next add the lemon juice and peas, toss and simmer for a couple of minutes until peas are heated through adding more pasta water if needed to thin out sauce.
Roughly chop remaining toasted walnuts and sprinkle over pasta. Serve immediately, garnished with chopped parsley.