'Lead opposite' doesn't mean anything! You've split up the sentence wrongly. The actor Aaron Paul is the male lead. The term 'male lead' refers to the hero, or the most important male actor in a production. The male lead is said to play 'opposite' the female lead, in this case the actress Michelle Monaghan.

It helps to break it down to "male lead, opposite" So he's the starring male actor, co-starring with his female counterpart Michelle Monaghan.

It's an expression for "starring/co-starring with" someone. (Aaron Paul and Michelle Monaghan are the lead actors of the series).