Trim the chicken breast if required, then cube it into bite-sized pieces.
In a bowl whisk the egg white until it starts to become frothy, then add the cornstarch, salt, and pepper. Continue to whisk until well combined. Stir through the chicken breast and put aside until needed.
Cut the bell peppers into square pieces about the same size as the chicken. Finely dice the garlic.
Heat the oil in a wok over high heat. When it starts to smoke add the chicken and cook while stirring until light brown on the outside.
Add the bell peppers and garlic and continue to cook until the bell pepper starts to soften.
Add the soy sauce and chicken stock and stir while cooking until well combined. Serve immediately alone or with rice.