Preheat oven to 350°F (175°C). Grease loaf pan or line with parchment.
Mix “buttermilk”: Combine almond milk and vinegar; rest 2 minutes until curdled.
Mash bananas: In a bowl, mash bananas with a fork until mostly smooth.
Combine wet ingredients: Stir melted coconut oil, maple syrup, and vanilla into bananas and “buttermilk.”
Whisk dry ingredients: In another bowl, mix flour blend, baking soda, baking powder, cinnamon, and salt.
Fold together: Pour wet mix into dry; stir gently until just combined.
Add walnuts: Fold in nuts if using. Do not overmix.
Bake: Transfer batter to pan; bake 50 minutes or until a toothpick comes out clean.
Cool: Let bread rest 10 minutes in pan, then transfer to a rack before slicing.