Preheat oven to 325º
To make streusel, combine first three streusel ingredients, then mix in butter until crumbly, and set aside
In a small mixing bowl, combine flour, baking soda, pumpkin pie spice, and salt and set aside.
In a larger bowl, whisk both sugars, and oil together
Add pumpkin and egg and whisk until smooth
Stir in zucchini
Add dry ingredients, and stir until just combined
Fold in walnuts or pecans if using
Pour batter into a greased 9x13 loaf pan
Top with streusel
Bake in preheated oven for 75 minutes, or until toothpick inserted in center of loaf comes out clean
Remove from oven and let cool 10 minutes
Loosen edges of loaf from pan with a butterknife or icing spatula, and remove from pan to finish cooling on a wire rack.