Prepare the Ingredients:
Measure out all your ingredients. If you're using frozen banana pieces, they can help thicken and chill the shake.
Blend the Oats:
Start by blending the rolled oats in the blender until they reach a fine powder consistency. This helps ensure a smooth texture for your shake.
Add Liquids First:
Pour the milk into the blender over the ground oats to help reduce sticking of the oats to the sides.
Combine Remaining Ingredients:
Add the protein powder, banana, peanut butter, honey, Greek yogurt, flaxseeds or chia seeds, and optional spinach and avocado to the blender.
Blend Until Smooth:
Blend on high until all the ingredients are thoroughly mixed and the shake is smooth. If the shake is too thick, you can add a bit more milk or some cold water to adjust the consistency.
Serve:
Pour the shake into a large glass or shaker bottle. If desired, you can add a few ice cubes to the glass for extra chill.