Place the flour in a shallow bowl and season with salt and pepper. Place the egg white in a separate bowl and whisk gently.
Dip the chicken pieces in the flour, then in the egg white, then in the flour again.
Heat 4 tablespoons oil in a wok or large skillet on medium high heat. When the oil is hot add the chicken pieces and cook briefly, turning once, until they are golden brown on both sides and just cooked through. Set aside.
In a small bowl, stir 2 tablespoons water into the cornstarch and whisk until smooth. Set aside.
In a saucepan, mix the jelly, soy sauce, brown sugar, vinegar and water and bring to a boil. Simmer gently, stirring, for 1-2 minutes.
Stir in cornstarch mixture and continue to simmer, stirring, until mixture starts to thicken.
In same wok or skillet that cooked the chicken, heat the remaining oil (adding more if necessary) and saute the garlic, until soft and fragrant, 1 - 2 minutes.
Add the guava sauce to the skillet and add the chicken pieces.
Heat chicken through, stirring to coat with the glaze.