Place sliced banana on a parchment paper lined baking sheet or cutting board. Place in the freezer until frozen, about 30 minutes to 1 hour.
Add all ingredients to a blender: frozen banana slices, pumpkin puree, yogurt, milk, ground flaxseed, maple syrup, pumpkin pie spice, cinnamon. Blend on low speed until smooth.
Taste for sweetness. Add extra milk as needed to thin to desired consistency. Enjoy!
Banana: If you don't love bananas in smoothies I recommend using a just-ripe banana (yellow/green peel) instead of a very ripe banana (spotty peel). This will decrease the sweetness and the banana flavor.
Greek yogurt: I use single-serve yogurt cups that are usually ~5 ounces. Plain yogurt, plain Greek yogurt and dairy-free yogurt also work.
Making the smoothie without frozen banana: You can omit the banana but the smoothie will be slightly less creamy. You can increase the amount of yogurt for a creamier smoothie. Add a few ice cubes for a colder smoothie.