That reminds me of an anecdote my uncle used to tell about a friend of his who had to return something he had borrowed from a Scottish friend of his. Knowing that the Scottish friend would be at work, my uncle's friend asked how he'd be able to return it. The Scotsman replied, "just stop by my house and knock up my wife."
My uncle's friend was greatly disturbed at the prospect.
Anyway, in response to the original question, I have usually heard "knock up [a meal]" in reference to something impromptu, like a soup, stew or chili. To me (Canadian English speaker) it would sound odd to "knock up some steak", or to "knock up some roast beef"; however, "knock up a beef stew" seems perfectly cogent.