1. Preheat the oven to 350°. Spread the walnuts in a pie plate and toast for 8 minutes, until fragrant and lightly golden; let cool. Chop 2 tablespoons of the walnuts.
2. In a large pot of boiling salted water, cook the broccoli rabe until tender, about 3 minutes. Drain and let cool under cold water. Squeeze out the excess water and coarsely chop the broccoli rabe.
3. In a food processor, mince the garlic. Add the 1/3 cup of walnuts; pulse until coarsely chopped. Add the broccoli rabe, olive oil and crushed red pepper and process until the broccoli rabe is very finely chopped. Add the 1/3 cup of pecorino and pulse until just combined. Season with salt and pepper. Scrape the pesto into a large bowl.
4. In a large pot of boiling salted water, cook the linguine until al dente. Drain, reserving 3/4 cup of the pasta cooking water. Add the linguine to the pesto sauce, then stir in the reserved cooking water and toss until the pasta is well coated with the pesto sauce. Sprinkle with the chopped walnuts and serve at once, passing more pecorino at the table.