My girlfriend thinks I'm weird, but I happen to like green apples in my Tuna. I only use water packed albacore and 'just' enough mayo to make it moist. None of that rancid non-fat mayo either, real mayo. Cube the apple into about 3/8" cubes and mix away with a wee bit of dill weed and squirt of lime juice. Sometimes I'll add horseradish too. I've been eating tuna for a long time, so one has to get creative after a spell, but it sure is hard to beat for a good, low fat, high protein meat.