That's called "spatchcock". It's a french technique and very good, you'll love it. It allows you to cook the bird much faster than if left in tact, plus easier to crisp up the skin.

Just my opinion, but: I don't think marinating in BBQ sauce will yield much of a result, as it won't penetrate the flesh. (mmmm flesh) I think you would probably enjoy it more if you marinated overnight in a Greek dressing. You could use Italian too, I guess.