Whisk egg in small bowl. Mix flour, salt, and pepper in another small bowl.
Dip cubed chicken in egg, then in flour/salt/pepper mixture to coat - Put in pan with preheated oil and fry in batches.
While chicken is cooking cube the green pepper and boil till tender. Drain and set aside.
Once chicken is done, make sauce:
In a medium saucepan put one cup of water and dissolve 1 bullion cube into it (or use 1 cup of chicken stock - either works). Add the juice from the can of pineapples, the soy sauce and the sugar. Mix the cornstarch into the vinegar before adding it to the sauce - it makes it easier to blend. Heat the sauce till thick and glossy. You will have to stir it often, especially when it starts to thicken.
Put the chicken, drained pineapples and peppers into a bowl - add the sauce and mix.