Prepare the Sauce:

In a saucepan, combine the white vinegar, apricot nectar, brown sugar, Worcestershire sauce, and ketchup.

Simmer for 30 minutes, stirring occasionally.

In a small bowl, dilute the cornstarch in a little water.

Gradually add this mixture to the simmering sauce, stirring continuously until the sauce thickens.

Set aside.

Cook the Chicken:

In a skillet, heat a little oil over medium heat.

Add the sliced chicken breasts and sauté without browning.

Add the green pepper slices, celery, and pineapple cubes to the skillet.

Stir constantly to mix the ingredients evenly.

Pour the prepared sweet and sour sauce over the chicken and vegetables.

Season with salt and pepper to taste.

Continue to cook, stirring occasionally, until the chicken is fully cooked and the vegetables are tender.