In a 5- to 6-quart pan over high heat, bring about 4 quarts water to a boil. Add couscous and cook just until tender to bite, about 6 minutes (10 for orzo). Drain and rinse under cold running water until cool.
Meanwhile, in a large bowl, mix vinegar and olive oil. Add couscous, radicchio, pistachios, parsley, and preserved lemon. Mix gently to coat, adding salt and pepper to taste.