Peel the banana and slice it into smaller pieces to make blending easier. Cut the avocado in half, remove the pit, and scoop out about one-quarter of the flesh. Measure the frozen mixed berries and other ingredients so everything is ready for blending.

Pour the water or almond milk into the blender first. Then add the Greek yogurt, banana slices, frozen mixed berries, avocado, and chopped walnuts. Placing the liquid at the bottom helps the blender process the frozen fruit smoothly.

Blend on high speed for about 45–60 seconds until the smoothie becomes completely smooth and creamy. If you prefer a thicker smoothie, add a few ice cubes and blend again briefly.

Pour the smoothie evenly into two tall glasses. Garnish with a few fresh berries or crushed walnuts on top for presentation. Serve immediately while the smoothie is chilled and creamy.