Preheat oven to 350°F. Lightly grease an 8x8-inch baking pan and line with parchment paper.
In a blender, blend banana and coconut milk. Pour in a large bowl and stir in coconut sugar and vanilla.
Add glutinous rice flour, baking powder, and salt. Mix until smooth and lump-free.
Pour batter into prepared pan. Tap on the counter to level.
Bake for 50–60 minutes, or until the top is golden and the edges pull slightly away from the pan. The center should be set but springy.
While baking, prepare buttercream. Whisk together butter, powdered sugar, vanilla, and non-dairy milk. Place strawberries in a blender or food processor and pulse until dust. Add the strawberry dust to the buttercream and stir until combined. Optional: Use a mesh strainer/chinois to remove the strawberry seeds before adding to frosting.
Once banana mochi has cooled, cut into 9ths and pipe buttercream on each square. Don’t forget the cherry on top!