Add the flax seed meal, frozen blueberries, banana, spinach or kale (if using), almond milk, yogurt, honey or maple syrup (if using), vanilla extract, ground cinnamon, and sea salt to a high-speed blender.
Blend the ingredients on high speed for 30-45 seconds or until smooth and creamy. If the smoothie is too thick, add more almond milk, a little at a time, until it reaches your desired consistency. If it's too thin, add a few ice cubes and blend until the desired thickness is reached.
Taste the smoothie and adjust the sweetness or seasoning if necessary. Add more honey or maple syrup for added sweetness, or a pinch more sea salt to enhance the flavors.
Once the smoothie has reached your desired taste and consistency, pour it into a glass or a to-go container, and enjoy immediately.