Is there a way to send a text message via voice command in iOS after dictating it?
If you have asked Siri to Send a new Message to some person, Siri Normally asks " Do you want me to send it" when it thinks you have finished.
Saying "Send" normally works. And Siri will say "Ok then I will send the Text message.."

I do not think there is a way to do it after you have used dictation.

Apples dictations command list