Preheat oven to 400 degrees Fahrenheit (200 degrees Celsius).

Wash the beets and put them on a dry baking sheet. Roast until a sharp knife pierces them easily, about an hour and a half or so. When the beets are cool enough to handle, slip their skins off. Use a serrated vegetable peeler, if necessary.

While the beets are still warm, dice them into one- to two-inch (2- and- 1/2- to 5-centimeter) squares. Toss with the couscous, breaking up any lumps with a fork. Combine with the chopped herbs and lemon zest.

Mix the spices with the olive oil and lemon juice and add to the salad. Toss well.

Refrigerate for at least an hour or two to allow it to chill completely, and for the flavors to mingle.

Add walnuts right before serving and toss well. Taste and adjust seasonings, if desired.

Garnish with more nuts and herbs before serving.