Cut the boneless chicken breasts into bite-sized pieces, ensuring they are uniform in size for even cooking.

In a bowl, combine flour, cornstarch, baking powder, and salt. Gradually whisk in ice-cold water until just mixed; avoid over-mixing.

Pour vegetable oil into a deep skillet or pot, filling it about three inches deep. Heat on medium-high until hot but not smoking.

Dip each chicken piece into the batter, allowing excess to drip off before placing it into the hot oil. Fry until golden brown and crispy, about 3-4 minutes per side.

Remove chicken from oil using tongs or a slotted spoon and transfer to paper towels to absorb excess oil.

Serve hot with soy sauce or spicy mayo on the side for dipping.