Preheat the oven to 180C/350F
In a large bowl mix pumpkin, sugar, oil and egg and beat with an electric mixer for 2 minutes.
In a separate bowl combine sifted flour, baking soda, baking powder, salt and all spices.
Add dry ingredients to the wet ingredients and mix until combined for about 2 minutes.
Make the butterscotch streusel topping by combining flour and all spices in a small mixing bowl, add softened butter and mix it with your hands until the mixture reminds large oat flakes.
Mix in chopped walnuts and butterscotch chips.
Line your loaf pan with some parchment paper or grease it well and pour the pumpkin loaf batter in it.
Top with the streusel topping and bake for 1 hour to 1 hour 10 minutes or until a toothpick comes out clean when the cake is pierced.
Cool in the pan for 30 minutes, then remove on a wire rack and cool completely.