Place the spinach or kale in a small microwave safe bowl with 1 tablespoon water. Microwave for 30-60 seconds. If you are using frozen spinach or kale it should be thawed, if you are using fresh it should be slightly wilted.
In a mini food processor, or blender mix egg, milk, prepared spinach or kale (see step 1) and banana until greens are finely shredded.
Pour into a medium bowl and add remaining ingredients. Mix until incorporated, but do not over mix. The texture should be very thick.
Pour batter into prepared donut pan. Bake 15 minutes or until a toothpick inserted comes out clean. Remove from the oven and allow to cool for a few minutes before removing from pan.