While having lunch, someone knocked on the door of our flat.Is that sentence right?

[abo.omar]

While having lunch, someone knocked on the door of our flat.
Is that sentence right?

 

[Tarheel]

While we were having lunch, someone knocked on the door of our flat.
Is that sentence right?

It is now.

 

[Yankee]

Yes.

 

[Yankee]

The sentence as posted would not be unusual in casual/common conversation.

 

[abo.omar]

It is now.

I want while followed by gerund.

 

[emsr2d2]

While having lunch, I was stung by a wasp.

If you want "While" to be followed by a gerund, the subject in the second clause needs to be the person who was "doing the gerund".

Note that "While having lunch, a wasp stung me" would be ambiguous. It suggests that it was the wasp who was having lunch.