A mono-meal in the purest form is a meal of only one type of food. So a meal that is 100% bananas. 100% apples. 100% watermelon.
Mono-mealers typically wait sufficient amounts of time in between consumption of mono-meals so that their meal digests undisturbed by other food. Different sources recommend different amounts of time in between meals depending on what they are. I think that it's probably ideal to eat 1 type of fruit per day in ample quantities. Ample quantities are likely more than you've ever consumed.
Do you think that adding potatoes to your orange juice is going to help digest them? Well you might say yes the orange juice has acid in it and that helps break down the potato starch. Well guess what, YOU MIGHT BE RIGHT! However, you are probably wrong and it will be a gassy nasty mess. Ripe organic sweet fruit digests best on its own. I have tried enough combinations to feel confident in this and I have tried enough mono-meals to feel that bliss.
22 bananas (2200 calories) in a sitting is literally no problem, but if I did something horrendous like mix an avocado and hemp seeds with apples and dates like newbie raw foodies might do I would not be able to consume more than 500 calories b/c that combo is horrendous and requires a digestive pH environment that can not exist in a single stomach.
If you want to be a successful 100% raw food-face it is best to learn simplicity and test it out. After you've spent many days being very physically active and just eating 1 type of food your confidence can actually come from more of a place of scientific clarity than just "eh well I feel gooder and such," but rather hey look I ran 25 miles and had a full work day and all I ate was orange juice. The next day I felt great etc... You can notice differences too, oranges have much more calcium and protein than bananas. You can build more muscle on the same amount of calories of oranges than you can with bananas. Though bananas may be much cheaper than oranges.
There are obviously many factors in a persons decision making matrix so please tell me what yours is so that I have a better idea about how people make their decisions: