Cut bananas into about 1" chunks. 
Freeze overnight
Process in food proccesor, will turn granular.
If adding liquid flavorings (vanilla extract for example) add now.
Bananas will eventually form ball, much like making dough.
Blend in optional mix-in ingredients
Your 'ice cream' should be soft-serve consistency, you can serve as-is or freeze for future enjoyment
Try mixing in:

• Splash of vanilla extract
• Shredded coconut and slivered almonds
• Rum extract & raisins
• Dark chocolate chips
• Coconut and crushed walnuts

Add your comments and tell us what you mixed in.
Note that dietary restrictions are impacted by what you mix in.  Checked restrictions are for basic recipe (bananas only).
Adapted from How to Cook Like your Grandmother