Preheat oven to 400°F. In a large bowl, whisk together flour, sugar, baking powder, cinnamon, and salt.
Add cold cubed butter and cut it in with a pastry cutter or fork until the mixture looks like coarse crumbs with some pea-sized butter pieces.
In a separate bowl, mash banana and whisk in milk, egg, and vanilla. Pour wet ingredients into dry and fold gently until just combined. Do not overmix.
Turn dough onto a floured surface and pat into a 1-inch thick circle. Cut into 8 wedges and place on a lined baking sheet.
Bake 15-20 minutes until lightly golden. Cool 5 minutes. Whisk glaze ingredients and drizzle generously over warm scones.