Preheat your oven to 400°F (200°C). Cube the cold unsalted butter and chop the rhubarb and strawberries.

In a food processor, combine all-purpose flour, baking powder, and salt. Pulse for 10 seconds until combined.

Add the cubed cold butter into the food processor and pulse until the mixture resembles coarse crumbs, about 15-20 seconds.

Transfer the flour-butter mixture to a bowl, and fold in the sugar, ground cinnamon, and lemon zest. Then mix in the chopped rhubarb and strawberries.

Gradually stir in the milk until a shaggy dough forms, about 30 seconds. Avoid over-mixing.

On a floured surface, pat the dough into a 10-inch circle about 1 inch thick. Cut into 8 wedges.

Transfer the wedges to a parchment-lined baking sheet. Brush each with egg wash made of whisked egg and milk.

Bake for 18-20 minutes until golden brown, and a toothpick in the center comes out clean.

Cool on a wire rack for 10 minutes. Prepare the glaze by mixing icing sugar, vanilla extract, and milk. Drizzle over warm scones.