To make the sauce, stir together all ingredients, except for the garlic, ginger, green onions and orange slices. Set aside.
Combine the egg whites, cornstarch, salt, sherry, baking powder and baking soda in a medium bowl and stir to combine. Pour over chicken in a sealable plastic bag and refrigerate for at least 30 minutes. Remove the chicken pieces from the bag, shake off the excess liquid, and give them another roll in some cornstarch (this will create a thicker coating).
Heat some high-heat, neutral-tasting on high in a wok, deep fryer, or heavy skillet and carefully lower the chicken into the oil. Fry until crispy golden brown on all sides. Using a slotted spoon, transfer the chicken pieces to paper towels to absorb the oil.
Reduce the heat to medium-high and add another teaspoon or so of oil to the saucepan or wok. Saute the ginger and garlic for 30 seconds, then add the sauce. Bring the sauce to a boil. Reduce the heat to low and simmer for 10 minutes, stirring occasionally.
Add the chicken pieces (or prepared tofu) and green onions to the sauce, stir to coat, and bring the sauce to a low simmer and cook for 5 minutes. Serve immediately with steamed rice and fresh orange slices (optional).