In my chicken and tuna salads, I use low-fat or fat-free vanilla yogurt instead of mayo to hold the salad together. Then season with tarragon and, for a special treat, stir in a tablespoon or two of chopped pecans or almonds.
On the bread, instead of spreading something I put on a layer of thin apple slices - moist, sweet and crunchy! **yum**
Of course, I've then got to use all the salad within a day or two, as yogurt doesn't seem to last as long as mayo. Since I don't mix up very much at once, it's rarely a problem.