If your different pawns will be of different classes, yes. If they will simply be different instances of the same class, interfaces are not necessary. You can just cast the GetControlledPawn to your pawn class and call functions directly.
Even if you have different pawn classes, ideally they should inherit from the same base class, so you can just cast to that base class and have the functions present in that base class. Especially for things that for sure will be common/shared functionality like movement.