Preheat oven to 350 degrees F (175 degrees C) and line a 12-cup muffin tin with liners.
Whisk flour, baking powder, baking soda, and salt together in a bowl.
Mash bananas with milk and vanilla extract until smooth.
Mix butter and sugar together with a spatula until creamy. Whisk in eggs, 1 at a time, then whisk in the banana mixture. Add walnuts, chocolate, and the flour mixture. Mix batter with a spatula until no dry spots remain.
Fill muffin cups to the top with batter, then distribute excess batter as needed. Tap pan against the counter to expel any air bubbles.
Bake in the preheated oven until tops are lightly browned, about 25 minutes. Let cupcakes cool to room temperature, at least 20 minutes.
Pour hot cream over chocolate chips in a bowl. Let sit for a few minutes, then whisk, increasing speed gradually, until color is uniform. Spread ganache over the cooled cupcakes and garnish with banana chips. Refrigerate to firm up the frosting, if desired.