I don't approve of slapgates.. men or women.. no gender bias there.. especially in a country like India, men slapping women on tv shouldn't be endorsed by anyone...
no matter what evil deeds lead up to such circumstances.. my personal opinion is that upon discovery, Asad should infact not really slap her or give her gyaan, but simply convey that, tannu has abused the beautiful relationship they shared ( according to him ) to a point of no return. It's better she go away from his life forever and leaves no traces of her ever being part of his life.
That said, simply maintain stoic silence. If Asad's inability to profess his love for Zoya or his silence in matters of love is making life unbearable for QH fans, I guess his silence born out of pure hatred will be enough to deal with Tannu.
Also, I don't think people should hate Tannu as much. She just has a twisted mind who thinks doing wrong and evil will justify all the wrongs done to her- read public humiliation and deserted by the father of her child, even if that is a direct result of her own wrong doings.
You choose a life and a path and should be willing to live with the consequences. That's how a normal and sane person's brain functions. Quite obviously that's not the case with Tannu. Because we love Zoya, we HATE Tannu, but she also needs our sympathy because she is abnormal and needs psychiatric help.