Dissolve the water in the salt and add the garlic and the chicken, meat side down, so that the meat is submerged in the brine. Let it stand for about 30 minutes.
Meanwhile, preheat the oven to 375 degrees. Drain the brine solution and dry the chicken on a paper towel. Place on a rimmed baking sheet lined with aluminum foil. Bake for about 30 minutes, until the chicken reaches a temperature of 165 degrees.
Set aside until it’s cool enough to handle and then chop it pretty finely.
While the chicken is cooling, prep the rest of the ingredients.
Finely chop the onion and pour enough boiling water to completely cover the onions. Let it stand for about 10 minutes. Drain through a sieve, rinsing with cold water.
Lightly beat one egg in a bowl, adding a pinch of salt and pepper. Heat a nonstick skillet, add about a teaspoon of butter or oil. Add the egg, tilting the pan so that the egg covers the whole surface, just like when you’re making crepes. Cook for about a minute the first side and about 30 seconds on the second side. Repeat with the rest of the eggs.
Stack the egg crepes on top of each other and roll them up tightly. I usually do half at a time. Slice it very thinly into little egg noodles. Run your knife through the egg strips the other way too. You don’t have to cut them too small, since the eggs will break more as you toss the salad together.
Julienne the cucumbers and finely mince the celery.
Combine all the ingredients in a bowl, adding the mayonnaise, mustard and freshly ground black pepper.
Scoop out portions of the chicken salad into each tart shell.