Bring a large pot of salted water to a boil. Add the rigatoni and cook according to package directions until al dente. Drain and rinse under cold water to stop the cooking. Let cool completely.

While the pasta cooks, heat a small dry skillet over medium heat. Add the chopped walnuts and toast, stirring frequently, until fragrant and lightly golden, about 3-4 minutes. Set aside to cool.

In a small bowl or jar, combine the olive oil, lemon juice, lemon zest, minced garlic, dried oregano, salt, and pepper. Whisk or shake until well emulsified.

In a large mixing bowl, combine the cooled rigatoni, crumbled feta, dried cranberries, toasted walnuts, diced cucumber, and chopped parsley. Pour the lemon vinaigrette over the top and toss gently until everything is evenly coated.

Transfer the salad to a serving bowl. Garnish with extra parsley or a few whole walnuts if desired. Serve immediately or refrigerate for 30 minutes to allow flavors to meld.