In a mixing bowl, add the chicken breast, soy sauce, salt and pepper.
In a separate bowl, add the flour, cornstarch, and baking soda and mix well. Make a well in the center and add the egg and soda water. Gently mix until combined.
Add the oil to a deep pot or saucepan and place it over medium heat.
Moving quickly, dip the chicken in the batter until fully coated. Shake off excess batter.
Place several chicken pieces in the hot oil and fry for 2-3 minutes until golden. Remove the cooked chicken and place them on a paper towel to soak up excess oil. Repeat the process until all the chicken is cooked.
Notes
Air fryer and oven instructions in the body of the post. TO STORE: Leftovers can be stored in the refrigerator, covered, for up to five days. TO FREEZE: Place the cooked and cooled tempura in an airtight container and store it in the freezer for up to 6 months. TO REHEAT: Either reheat tempura in a non-stick pan or in the air fryer/oven. Do not microwave them as they will be soggy.