Stir the couscous, cranberries, curry powder, salt, and sugar together in a heatproof bowl. Bring water (amount will be listed on package directions) to a boil and pour it over the couscous. Add the orange juice. Give it a big stir, cover the bowl tightly and let it stand, giving it a big stir once or twice, until the water is absorbed and the couscous is tender, about 5 minutes.
Fluff up the couscous with a fork. Add the olive oil, scallions, parsley, lemon juice, and walnuts. Stir around until everything is distributed evenly throughout the couscous. Make up to 2 hours ahead of time and keep at room temperature until you're ready to serve. Check the seasonings just before you serve the salad and add salt and pepper, to taste.
To toast the walnuts, spread them out on a baking sheet and bake in a 400 degree F oven until they turn a shade darker, about 8 minutes.