Preheat oven to 350 degrees Fahrenheit. Line a muffin tin with non-stick muffin liners and set aside.
In a high-speed blender or food processor, add all ingredients except for blackberries and process until smooth, being careful not to overmix.
Using a spoon, gently stir the blackberries into the muffin batter.
Scoop the batter into non-stick muffin liners so they are filled right to or just below the rim. Top each muffin with some banana slices and 1-2 blackberries, if desired.
Bake in the oven for approximately 20 minutes or until a toothpick comes out clean when inserted into the middle of a muffin.
Notes
Fridge: Store leftover muffins in an airtight container in the fridge for up to 4 days or on the counter for 1-2 days. Freezer: Allow muffins to cool completely before storing. Once cooled, transfer to a freezer-safe airtight container or freezer bag for up to 3 months. Thaw on the countertop at room temperature or heat the frozen muffin in the microwave until heated through. You may want to heat the muffins in the oven for a few minutes to get them a little crispy/firm on the outside again.