Heat the oil in a wok or large frying pan until very hot.
Whilst the oil is heating, place the egg in one shallow bowl and the cornflour in another shallow bowl. Add the flour, salt, pepper, garlic salt and paprika to another shallow bowl and mix together.
Dredge the chicken in the cornflour, then dip in the egg (make sure all of the chicken is covered in egg wash), and finally dredge it in the seasoned flour. Add to the wok and cook on a high heat for 6-7 minutes, turning two or three times during cooking, until well browned. You may need to cook in two batches (I find I can do it in one batch so long as it's no more than 3 chicken breasts). Remove from the pan and place in a bowl lined with kitchen towels.
Whilst the chicken is cooking, you can start on your sauce.
Add the oil to a large frying pan/skillet, heat it up on a medium-to-high heat and add in the onions. Cook for 3 minutes, stirring every now and then, until the onions start to go translucent.
Add the peppers and cook for a further minute.
Add in the garlic and ginger and cook for another minute. Add the tomato ketchup, vinegar, dark brown sugar, and the tinned pineapple (including the juicand stir. Bring to the boil, and then turn down the heat and let it bubble (stirring every so ofteuntil slightly thickened.
Transfer the cooked crispy chicken to the pan with the sauce and toss to coat.
Serve with boiled or fried rice and a sprinkling of sesame seeds.
Nutritional Information is per serving including sesame seeds, but not rice (I don't know how much rice you're going to serve this with :-))