Use a can opener to open the cans of tuna. Then, over a sink, use the lids pressed against the upside-down cans to squeeze out and drain the liquid (there will be some liquid left in the tuna; that's OK). Transfer the tuna to a medium bowl.

Add sliced shallot and lemon juice to bowl, along with 2 tablespoons mayonnaise, 1/2 cup shaved Brussels sprouts, a good sprinkling of salt and a few cracks of pepper. Taste. If desired, add more mayonnaise, shaved sprouts, lemon juice, salt and/or pepper.

Serve on (toasted or untoasted) bread, with crackers, in an avocado half, etc.