Heat oven to 350°F (175°C); parchment-line sheet.

Whisk flour, baking powder, and salt in bowl.

Cream butter and brown sugar smooth; beat in banana, egg, and vanilla.

Mix in dry just until combined; fold in walnuts and optional chips.

Shape log about 12 x 3 inches on sheet; flatten slightly.

Bake 25–30 minutes until golden; cool 10 minutes and slice 3/4 inch thick.

Arrange cut-side down; bake 10–12 minutes more per side until crisp. Cool completely.