I can't go along with "Just action!", I'm afraid. This kind of statement requires a verb, and although "to action" is a verb (if you must!) it's used transitively; in any case is not suitable in this context. I guess you could say "Just act!", but that would not be particularly idiomatic, and is also ambiguous (i.e. as in "pretend"; "play a part").
'action' used as a verb is, in my experience, only used as business jargon. It means 'do' but business people love to contort the English language and use other words to make things sound important. To 'action' something would not be used in everyday language.