In Nalo Hopkinson's short story Shift, Caliban has a relationship with a "golden girl". At some point, Caliban mentions she is cooking oats. At an earlier point in the story he says
There was a time they called porridge “gruel.”
I have no idea how this fits into the rest of the story. The Wikipedia article about porridge explains that, "Historically, porridge was a staple food in much of Northern Europe, North Korea, and Russia." The Wikipedia article about gruel says that,
It is a thinner version of porridge that may be more often drunk than eaten and may not need to be cooked. Historically, gruel has been a staple of the Western diet, especially for peasants.
The article also contains a paragraph on the etymology of "gruel". That does not really help, nor does the article about oatmeal.
After analysing the story for answers to two other questions, I am convinced that it is too carefully crafted for this porridge remark to be meaningless, but I cannot come up with an explanation for its presence in the story.
Addition: I don't know whether this is relevant, but in Shakespeare's works, "gruel" is apparently only used in Macbeth, Act IV, where the "Third Witch" says, "Make the gruel thick and slab". "Porridge" is used in The Tempest, Act II, scene, where Sebastian says about King Alonso, "He receives comfort like cold porridge.". The word "porridge" also occurs in several other Shakespeare plays (e.g. 1 Henry VI and Troilus and Cressida).