Preheat oven to 400°. Line 2 rimmed baking sheets with parchment paper.

In a large bowl, whisk together flour, sugar, baking powder, and salt. Using a pastry blender or 2 forks, cut in cold butter and cold cream cheese until mixture resembles coarse crumbs. Add walnuts, stirring until combined.

In a small bowl, stir together mashed banana and pineapple. Add banana mixture to flour mixture, stirring until mixture is evenly moist.

Turn out dough onto a heavily floured surface. Using well-floured hands, knead gently until a smooth dough forms, 5 to 10 times. Roll dough to a ¾-inch thickness. Using a 2-inch fluted round cutter, cut 18 scones from dough, rerolling scraps as necessary. Place on prepared baking sheets. Freeze for 10 minutes.

Brush tops of scones with beaten egg.

Bake until edges of scones are golden brown, 16 to 18 minutes. Let cool slightly on a wire rack. Serve warm.