Place your frozen banana, pumpkin puree, cashew butter, pumpkin pie spice, and protein powder into a high-powered blender. Pour in a small splash of milk to help things move before you start blending.
Blend everything on high until it looks completely smooth with no visible banana chunks left behind. The mixture should be noticeably thick, almost like soft-serve, not thin like a regular drinkable smoothie.
If your blender is struggling or the mixture looks too stiff to move, add a small splash more milk or water. Go slowly here, since it's much easier to loosen a thick bowl than to fix one that's turned too watery.
Once it's fully blended and thick, pour or spoon the mixture into your serving bowl. Use the back of a spoon to smooth the top so your toppings have a nice, even surface to sit on.
Arrange banana slices, pepitas, and granola over the top in whatever pattern looks appealing to you. Serve immediately, since smoothie bowls soften quickly and taste best ice-cold.