Lately I've been enjoying something called "Spuma di Tonno" from _Casual
Cooking_ by Michael Chiarello. I eat it on slices of European cucumber--the
long, unwaxed ones that come in plastic wrap in the supermarket--although
homegrown cucumbers without wax would also be great. (Of course, many other
crisp vegetables, such as red peppers and pea pods, would be fine, too.)
Non-diabetics would like it on something like crackers, grissini, or bagel
crisps of course.

Here's the recipe:

2 5-oz cans of Italian-style tuna packed in olive oil, drained
1 Tbs fresh lemon juice
1 Tbs soy sauce
1 Tbs balsamic vinegar
2 Tbs unsalted butter, softened
Sea salt and fresh black pepper
1 1/2 Tbs heavy cream

Put fish in food processor. Pulse to break up. With the machine running, add
lemon, soy, and vinegar. Add butter and blend until smooth. Scrape down the
sides, season to taste with salt and pepper, and blend again. Add cream and
pulse to blend. (Don't overblend after adding the cream or the mixture might
break.)

Serve at room temperature or slightly chilled. Keeps covered in the fridge
for several days. (I don't really know how long it lasts because it's always
gone in a day here.)

This is very flavorful and both cheaper and a lot less calorific than smoked
trout mousse, my other spread of choice for cucumber slices.