Preheat the oven to 375°. Line two muffin tins with paper liners or spray with nonstick cooking spray.
In a large mixing bowl, combine the buttermilk, oil, and eggs.
In another large bowl, whisk together the flour, sugar, baking powder, orange zest, salt, and cinnamon. Fold the dry ingredients into the wet. Add the raspberries and gently fold them in.
Divide the batter into the 24 muffin cups of the pan.
Prepare the nutty streusel by working together the flour and butter with a pastry blender until coarse crumbs are formed. Work in the brown sugar. Then stir in the nuts.
Sprinkle the streusel over the tops of the muffins.
Bake until golden brown and a tester inserted comes out with a few crumbs attached, about 20 minutes. Cool on a rack.
To freeze: cooled muffins can be stored in an airtight container in the freezer for up to 2 months.
Nutritional values are approximate and are based on 1 muffin. Use within 3 days or freeze for longer storage.Muffins can also be frozen unbaked. Place lined tray in freezer until batter is solid. Remove muffins from the tray and place in an airtight container in the freezer. Bake as directed when ready to serve.