With a rolling pin, flatten out the slices of bread so they are extremely thin and easily foldable. Set aside.
In a large bowl, add cooked chicken, onions, bell peppers, garlic powder, mayonnaise, mustard, and salt and pepper to taste. Stir to combine the ingredients together.
Place a scoop of the chicken filling to one of the rolled-out slices of bread. Roll the bread over the filling, enclosing it completely, and using a toothpick to hold if needed. Repeat until all of the bread slices are filled.
Set a large pan over medium high heat with olive oil. Dip each roll with beaten egg then set on pan, making sure to leave some space between each roll.
Cook each side for about 1 to 2 minutes or until the bread rolls are golden brown.
Remove from the pan and let them cool for a few minutes before serving.