This is my favorite treat!

Cut up a banana and put it in the freezer before you go to the gym. When you get back (or in 1-2 hours) mash up the banana with a handblender (a normal blender might work also) until it is icecream consistency. Add nutmeg and cinnamon or vanilla extract if you want. I usually blend in a raw egg yolk, but I'm weird.
Frozen raisins are good in it also if you want more sugar.