This is based on a classic Italian salad that can be thrown together with pantry items. All you need from the market is the cucumber, which makes a beautiful garnish for the high-protein tuna-and-bean mix.
SPIRALIZING THE ONION: Use the shredder blade. Insert the onion into the spiralizer blade at the root end. Take up handfuls of the spiralized onion and cut into 2- to 3-inch lengths with scissors.
SPIRALIZING THE CUCUMBER: Use the slicer blade. Take up handfuls of the spiralized cucumber and cut into 2- to 3-inch lengths with scissors.
Place the spiralized onion in a bowl and add 1 teaspoon of the vinegar and cold water to cover. Let stand for 5 minutes. Drain and rinse with cold water, then dry on paper towels.
In a medium bowl or salad bowl combine the tuna, beans, onions, sage, and parsley.
Mash together the anchovy and garlic in a mortar and pestle. Add the remaining vinegar, the lemon juice, salt to taste, freshly ground pepper, and Dijon mustard, and mix together. Whisk in the olive oil or work in with the pestle.
Set aside 1 tablespoon of the dressing. Toss the rest with the tuna and beans. Toss the spiralized cucumbers with the remaining dressing. Arrange the tuna-and-beans salad in a bowl or on a platter, and top with the cucumbers.
ADVANCE PREPARATION: The tuna-and-beans salad, without the cucumbers, will keep for a couple of days in the refrigerator.