In a large bowl, whisk together flour, pumpkin pie spice, salt, and baking soda. Stir in the sugar.
In a separate bowl, combine pumpkin puree, vegetable oil, yogurt, eggs, and vanilla extract.
Slowly mix the wet ingredients into the dry ingredients until combined. It's okay if it's slightly lumpy!
Pour loaf mixture into greased pan.
In another small bowl, mix together 1/2 cup flour, 3 tbsp sugar, 3 tbsp brown sugar, and 1/2 tsp cinnamon for the streusel topping.
Gradually pour melted butter over the streusel mixture, using a fork or spoon until clumps start forming (be careful not to stir too much.)
Sprinkle streusel topping over unbaked loaf mixture and then bake in the oven for 55-60 minutes or until a toothpick inserted into the center comes out clean.
Notes
I'm pretty sure this works at both high altitude and sea level, but I've only tested at high altitude (5280 feet.)