Cold Cucumber-Walnut Soup

1 cup shelled walnuts
6 large cucumbers, peeled, seeded, and thinly chopped
2 large cloves garlic, minced
1 quart buttermilk
1 1/2 tablespoons finely minced dill
1 teaspoon salt
1/2 cup finely chopped scallions, including green tops
Juice of 1 lemon
1 1/2 cups plain nonfat yogurt
1/4 teaspoon white pepper

Place walnuts on a cookie sheet. Roast in a preheated 350