Naturally, a Google search reveals all.
Here are the ones I found, making this into an aggregator post, really:
Dave Hood’s Find Your Creative Muse (1018 words, May 2012). He defines Theme, and has 4 paragraph points on how Theme is revealed. List of resources on books on theme/writing at the end.
Here’s a blurb from Larry Brooks’ Story Engineering at Writer’s Digest (588 words, April 2012). I knew it looked familiar.
Fiction Editor Beth Hill on The Editor’s Blog (1261 words, October 2010) lays out a good definition of Theme. She also has a laundry list of ideas at the end.
I wanted to see what Kristen had done on this, and found these:
Charles Dickens—Using Symbol, Theme & Allegory to Create Enduring Stories (2269 words, December 2015)
Symbolism & Setting—The Perfect Marriage (1054 words, June 2016) with guest bloggers Angela Ackerman and Becca Puglisi.
Purdue Online Writing Lab has an entry here, contributed by Kenny Tanemura (1038 words, November 2011).
Melissa Donovan on Writing it Forward has Fiction Writing Exercises for Exploring and Developing Theme (1148 words, October 2015). Writing exercises? Yes. Work out theme-writing muscles.