Firstly, lay the chicken breast out on a large square of cling film. Cover with another square of cling film then, using a rolling pin, bash the fillet out until flat.
Remove the top layer of cling film then, using a palette knife, spread the garlic butter all over the chicken.
Using the bottom layer of cling film as a guide, roll up the chicken like you would a swiss roll. Wrap tightly in cling film, then refrigerate until ready to cook.