Rhubarb Ginger Downside-Up Oatmeal Cake

Many, many thanks for this lovely recipe. I made minimal changes--I used half chopped tart apple, half rhubarb and baked it in a good, heavy cake pan instead of the cast iron. It was absolutely fabulous. Everyone raved and, as the name (especially with addition of apple) is a bit unwieldy, the youth vote was to call it "Unicorn Cake." I have already received multiple requests for more unicorn cake. BTW, my fresh ginger was living in the freezer--I grated it frozen and it was perfect. Maybe this is a little astuce known to everyone, but I was delighted to discover it.