Cut chicken into ~1-inch pieces. Pat dry.
In a flat plate or bowl, combine flour, corn flour and salt. In a bowl, whisk egg.
Add chicken to egg mixture. Mix to coat well. Then coat each piece of chicken with flour mixture.
Heat up large skillet with vegetable oil. Make sure there is a thin layer of oil covering the entire surface of the skillet.
Once oil is heated up, add chicken pieces to skillet. Do not overlap or overcrowd skillet; cook in two (or three) batches if necessary. Cook under medium heat and cover if necessary,
Flip chicken over once one side is cooked. Cover again if necessary. Do not overcook chicken. Chicken is cooked once internal temperature reaches 165 degrees F. Remove chicken from skillet and set aside.
If skillet has a lot of burned flour pieces from cooking the chicken, use a paper towel to remove/wipe it off before proceeding.
Heat skillet and add more vegetable oil if necessary (we don't need a lot for this). Once oil is heated, add bell peppers and onions to skillet and stir fry for ~1 minute under medium heat. Do not overcook the vegetables. The goal is to slightly soften the vegetables so it is not completely raw. Remove promptly.
Add sauce ingredients to skillet, stir and let it come to a boil. Lower heat and let it simmer for a minute or so, or until sauce thickens slightly.
Bring cooked chicken, cooked bell peppers, cooked onions, and pineapple pieces back to skillet. Toss chicken and veggies with sauce. Remove from heat promptly.
Serve with rice. Enjoy!