One double-spaced, typed research paper is really quite brief; however, the challenge for you is to keep your thesis (the argument you intend to prove) rather narrow. For example, you might focus on a specific character trait of a figure from a novel or short story you have recently read--something about which you are already comfortable writing--and how that trait, say a physical characteristic like a limp or a scar, reveals that character's true nature.
In another approach, you might describe the tone or mood (these are two different qualities, so be sure you understand which is which) of a particular poem or story and how that tone or mood influences our understanding of an important theme the piece is addressing.
In either case, if this is a research assignment, your professor will expect you to have researched authoritative support (like that you find amid the literary criticism on Enotes!), to have cited, either in paraphrase or direct quotes, the opinion of your literary expert in the body of your researched essay, and to have properly documented that source according to MLA documentation guidelines. These guidelines are easy enough to follow, and you may learn more about them by visiting the Purdue University OWL (Online Writing Lab), which is freely available to the public. Just Google them up!