Put enough oil in a large skillet to have it two inches deep. Place on burner, turn heat to medium high and let the oil preheat.
Mince the garlic, and mix it in a bowl with the soy and sherry. Cut the chicken into 1 inch pieces, place in bowl with garlic, soy and sherry and stir to coat.
Zest two of the lemons and set the zest aside.
Juice and strain all of the lemons and place the juice in a small saucepan.
In a flat dish, mix the flour, lemon zest, salt and pepper. Toss the chicken pieces in the flour to coat. Fry the chicken until golden brown, making sure not to crowd the pan. Remove from pan and drain on paper towels. You will probably have to cook the chicken in 3 batches.
While the chicken is cooking, mix the water or stock and the corn starch in with the lemon juice and cook over medium heat until it starts to bubble, stirring constantly, until it starts to thicken. Do not let it thicken too much. It should be glossy and almost clear. Salt to taste.
Divide the chicken pieces into 4 and place on plates. Pour desired amount of sauce over chicken and serve over rice or with a green salad.