Add the water, orange juice, and spinach into the blender and blend until the greens are completely broken down. This will ensure you don't get bits of greens in your final smoothie. If you are adding in any of the optional add-ins, like almond butter or hemp hearts, you should blend them during this step, too.
Add in the frozen banana and mango, and blend again until smooth and slushy. Serve right away for the best texture and flavor.
The orange juice adds sweet and tart flavors to this smoothie, which make it taste really great. As an alternative, you can use a whole peeled seedless orange instead. Or, you can add a squeeze of fresh lemon juice and a pitted Medjool date for similar sweet and tart flavors.