This is a very fun, creative question. Given the fact that there are some highly quotable (and somewhat pithy) moments in the text of the novel, I'd suggest that we might look for quotations from The Great Gatsby itself for a title idea or two.
Here is a passage from early on in the text, pulled from the eNotes page of quotes from Gatsby:
"If personality is an unbroken series of successful gestures, then there was something gorgeous about him, some heightened sensitivity to the promises of life.… [Gatsby had] an extraordinary gift for hope, a romantic readiness such as I have never found in any other person and which it is not likely I shall ever find again."
From this extended quote, we might take the phrase "An Unbroken Series of Gestures" as a potential title for an essay on Gatsby's ill-fated quest to recapture the past. Alternatively, we could isolate the phrase "An Extraordinary Gift for Hope" as a title on the same subject.
Each of these phrases resonates with (1) the notion that Jay Gatsby is dedicated to a romantic and, arguably, highly unrealistic view of reality and (2) that Gatsby's greatest flaw was also his greatest virtue - the ability to dream.
This vision of Gatsby is repeated in several places in the novel and given a clear rendition when Nick confronts Gatsby on the subject of his quest.
“You can’t repeat the past.”
“Can’t repeat the past?” he cried incredulously. “Why of course you can!”
Using "Can't repeat the past?" as a title, your essay might start at the very beginning by using Gatsby's own words to describe his impossible aims. Gatsby is "The American Dreamer" dreaming the American dream, as is often pointed out in discussion of Fitzgerald's novel. So, using the idea of dreams and dreaming might also be a good way to go for the title of an essay on Jay Gatsby's romantic, idealistic and ill-fated quest.