imageViewにはbackGroundImageのプロパティはないので
あらかじめ用意したimageViewにimageViewをのせます
let backImageView = UIImageView()
backImageView.image = UIImage(named: "haikei")
backImageView.frame = CGRect(x: 0, y: 0, width: view.bounds.size.width, height: view.bounds.size.height)
backImageView.contentMode = .scaleToFill
let imageView = UIImageView()
imageView.frame = CGRect(x: 0, y: 0, width: view.bounds.size.width, height: view.bounds.size.height)
imageView.contentMode = .scaleAspectFit
backImageView.image = UIImage(named: "image")
imageView.backgroundColor = .clear
backImageView.addSubview(imageView)
view.addSubview(backImageView)
できると思います
参考になったらいいですね