In a blender, blend 1/2 banana, 3 oranges and 1/2 cup Greek yogurt until smooth and incorporated. Taste and add more bananas, if you want your smoothie creamier or sweeter. If you want to thin it out, add a teaspoon (or more) of milk.
To freeze bananas, I slice them into 1-inch thick pieces, put them in a Ziploc bag and store them in the freezer until I'm ready to use them. I label the bags - how many bananas there are (e.g. 1/2 or 1 whole) and the date I froze them.
Bananas have a very strong flavour and tend to overwhelm other fruit flavours in a smoothie. For this recipe, start with 1/2 of a banana and add 1-2 slices depending on the flavour and texture you want.
For this recipe, I used Cara Cara oranges but you can use whatever kind of orange you like. Just remember that different oranges have different flavour profiles. Taste and adjust as you build your smoothie.
Oranges tend to dry up when frozen for too long. So to freeze oranges for this recipe, simply put the supremed slices in a Ziploc bag and place them in the freezer about an hour before you plan to use them. This is enough time to chill them while still preserving their wonderful juices.
You can also choose to just juice the oranges instead of putting in whole wedges/slices.