Prep your produce. Rinse spinach and pat dry.
Core the apple and chop into chunks. Slice cucumber into pieces. Peel the lemon and ginger.
If using a juicer: Run the spinach, apple, cucumber, lemon, and ginger through the juicer in that order.
Stir the juice to combine.
If using a blender: Add spinach, apple, cucumber, lemon, ginger, and 1/2 cup cold water to the blender. Blend on high until very smooth, 45–60 seconds.
Strain for a smooth texture. Pour the blended mixture through a fine-mesh sieve or nut milk bag into a bowl or pitcher. Press or squeeze to extract the juice.
Add more water if needed to reach your desired consistency.
Taste and adjust. If it’s too tart, add a few extra apple slices. If you want more zing, add a bit more lemon or ginger.
Serve cold. Pour over ice if you like it extra crisp. Drink right away for the brightest flavor.