Preheat the oven to 400°F and line a baking sheet with parchment paper to prevent sticking.
Whisk together the flour, sugar, baking powder, salt, cinnamon, and nutmeg in a large bowl until evenly combined.
Cut the cold butter into the flour mixture using a pastry blender until the texture resembles small crumbs, then freeze the mixture briefly to keep the butter cold.
Fold the frozen rhubarb into the flour mixture so it distributes evenly throughout the dough.
Whisk together the heavy cream, vanilla extract, and most of the orange zest in a separate container until smooth.
Create a well in the center of the dry ingredients and pour in the cream mixture, stirring gently just until the dough comes together without overmixing.
Turn the dough onto a lightly floured surface and gently press it into an even round shape about 8 inches wide.
Cut the dough into wedges using a sharp knife and place the scones onto the prepared baking sheet with space between each one.
Brush the tops with heavy cream and sprinkle generously with turbinado sugar for a crisp finish.
Bake until the scones are golden brown and cooked through, then let them cool slightly on a wire rack.
Whisk together the powdered sugar, remaining orange zest, orange juice, and a pinch of salt until smooth, then drizzle the glaze over the warm scones before serving.