So I revisited the "banana bread surprise" and made another batch, and this time, I was able to bake it in the GoSun. I lined the tray with parchment paper and poured the batter in directly, instead of using the silicone mini loaf pans. The quantity adapted to a 6' by 9' baking dish fit perfectly into the tray. It took about 40 minutes in the early afternoon sun. Everyone who tried some agreed that it was delicious. It was way better than the last batch, for which I had to use the toaster oven.
By my calculations you lose almost a third of the volume of the tray if you use the silicone baking cups. The same amount of batter fit into 11 mini loaf pans, of which only eight fit into the GoSun.