Prepare 24 muffin cups by spraying generously with cooking spray; set aside.
In a large bowl stir together 1 cup of the flour, the brown sugar, Clabber Girl Baking Powder, cinnamon, and baking soda. Add pumpkin, molasses, eggs, butter, milk, and ginger. Beat with an electric mixer on low speed for 30 seconds or until combined. Beat on medium to high speed for 2 minutes, scraping bowl often. Add remaining flour; beat about 2 minutes or until mixed.
Divide batter evenly among muffin cups. For Streusel topping, combine flour, brown sugar and cinnamon. Cut in butter with pastry blender and stir in nuts. Sprinkle evenly over batter in muffin cups. Bake in a 350° F. oven for 25 minutes, or until tops spring back when lightly touched. Cool in pans until muffins come out easily, about 20 minutes.