Pat the chicken thigh fillets dry with paper towels. Cut into 1½-inch cubes.
In a bowl, mix all the ingredients for the marinade until the sugar is completely dissolved.
Add the chicken to the marinade and mix well.
Cover the bowl and marinate the chicken in the fridge for at least an hour.
In a wok or frying pan, heat enough cooking oil to reach a depth of at least three inches. The ideal frying temperature is 350F.
While the oil heats up, make the batter by whisking together he corn starch, salt, pepper, chili powder and half of the flour. Stir in iced water to make a fairly thin batter (see notes after the recipe).
Toss the chicken in the remaning flour.
When the temperature of the oil reaches 350F (or, if you don't use a thermometer, you see fine wisps of smoke floating on the surface of the oil), it is time to start frying.
Dip each piece of floured chicken in the batter and drop in the hot oil. Cook the chicken in batches to avoid overcrowding which will result in temperature drop. The coating of the chicken should be lightly browned after four to five minutes of frying which is just enough time to ensure that the chicken is cooked all the way through.
Drain the cooked chicken and transfer to a mixing bowl.
Drizzle in the sweet chili sauce and toss to coat each piece of chicken with sauce.
Serve the sweet chili popcorn chicken over rice with your preferred greens on the side.