First off, I would recommend the employment of a competent electrician, to carry out this work.
Either way is suitable, just make sure you have sufficient depth box behind cooker outlet, 47mm minimum and that the faceplate can accept the cables you are going to terminate inside it. If this is a new kitchen, then the cables can be run in the service void behind the units, I normally use the plinth area. The only bit that would need flushing in, is between worktop and faceplate, unless your going for the rustic look!
By the by, the glass surface of a ceramic/induction hobs are a real nightmare to keep clean, even with propriety cleaners!