We were studying Einstein and fruit last month. For themes we tend to gravitate toward people and their historical context and then a non-human item, often unrelated, but sometimes not. There was Sacagawea and bridges a few months back and then Einstein and fruit and now we are on to Darwin and butterflies. They chose these themes and the mash-up is pretty funny. I often give a list of suggestions for the people (usually because I have a good biography stashed) and then the other topic gets announced. Or more often yelled with vigor.
So, after reading books about fruit trees, pollination, and all that, we all went to our nearby Asian market and picked out fruits, most of which were new to us. I wrote these all down and have the list somewhere. I was so happy I could do a quick search on everything we bought and see how to peel, cut, and eat it, because I had no clue for much of it and some of the skins and bits are not edible and will cause hives, or something else unpleasant.
The girls loved doing this. We had a big fruit tasting event, tried everything, they cut into them, smelled them, drew pictures of them and of course tasted them (they all did, even my most reluctant new foods eater, you know, in the name of science) and then we voted on the favorites. I took every last bit left over and saved it it the freezer for smoothies. This last shot is of the $10 dragon fruit. I am tempted to do this with veggies. And then fancy cheese.