2. Add chia seeds
Chia seeds like banana are an incredible binding agent, and also fantastic for thickening smoothies. Either simply add one tablespoon of chia seeds in with the other smoothie ingredients and blend, or create a smoothie gel.
To make a gel mix some chia seeds with water and leave to thicken, then mix in with smoothie. You can soak the chia seeds overnight, but even 10 minutes will do.