In a high-speed blender, combine the zucchini, banana, peanut butter, honey, and spinach, if using. Blend until smooth, adding a little extra water, if needed to keep everything blending. Taste and add an extra squeeze of honey, if needed.
Serve right away for the best texture and flavor.
Make Ahead Tip: For an easy smoothie bag, add the zucchini, banana, peanut butter, and spinach, if using, to a freezer bag, then store it in the freezer for up to 3 months. When you're ready to make the smoothie, dump the contents of the bag into your blender, add the water and honey, and blend until smooth.Nutrition information is for the whole batch, and is just an estimate, not a guarantee.