Make sure the chicken is cut into 1-inch cubes so that it cooks evenly. Place it in a 10-inch baking tray, and set aside while you mix up the sauce ingredients.
The sauce will thicken up because of the cornflour and mayonnaise, you can adjust the amount of cornflour and mayonnaise depending on how thick or thin the sauce you would like.
Just cook the chicken in a bit of oil in a frying pan or medium-sized pot, until it changes color, then add the seasonings - garlic powder, salt, and pepper and cook for a minute or so.