Preheat the oven to 350°. In a large saucepan of boiling salted water, cook the barley over high heat until tender, about 25 minutes. Drain the barley and rinse under cold water to cool thoroughly. Drain again, shaking out the excess water.
Meanwhile, spread the walnuts in a pie plate and toast for 10 to 12 minutes, until golden and fragrant. Transfer to a cutting board and let cool. Coarsely chop the nuts.
In a large bowl, whisk the lemon juice with the olive oil, garlic and lemon zest and season with salt and pepper. Add the barley, parsley and ricotta salata and toss gently. Add the toasted walnuts, toss again and serve.