I love this chilled soup from my cookbook, Gourmet Made Simple. It is also delicious topped with smoked salmon.
FIRST Preheat oven to 350°F. Toss tomatoes with olive oil and season with salt and pepper. Roast in oven for about 20 minutes or until tomatoes begin to blister and burst. When tomatoes are ready, remove from oven and set aside.
NEXT Combine avocados, cucumber, onion, lemon zest, and lemon juice in a blender or food processor. Pour in buttermilk and purée. Add stock, one cup at a time, until the soup is creamy but not too thick; season to taste with salt, black pepper, and cayenne pepper.
LAST Spoon soup into bowls (one cup each) and top with tomatoes.