Preheat the oven to 350°F (175°C). Line a 12-cup muffin pan with paper liners or lightly grease the cups.
In a large bowl, mash the bananas until mostly smooth. A few small lumps are fine.
Add the brown sugar, plant milk and melted vegan butter or coconut oil. Stir until well combined, about a minute or 2.
Add the flour, baking powder, cinnamon, and salt to the bowl. Gently fold the batter just until no dry streaks remain. Do not overmix; it should take about 2 minutes.
Fold in the vegan chocolate chips and chopped walnuts.
Divide the batter evenly among the 12 muffin cups.
Bake for 22-25 minutes, or until the tops are set and a toothpick inserted into the center comes out without wet batter. Melted chocolate is fine.
Let the muffins cool in the pan for 3 minutes, then transfer them to a wire rack to cool completely.
Notes
Room temperature: Store banana chocolate chip muffins in an airtight container for up to 3 days.
Freezer: Freeze for up to 2 months in an airtight container or freezer bag and thaw at room temperature.