That one meal a human can live on solely and remain healthy

Of course, a varied diet is the healthiest, but if forced to live on only one meal (which I interpret as a single dish) to survive, I would choose…

…a baked potato with sour cream and bacon.

The potato is practically the perfect food for humans, provided it is not served in the form of chips (crisps) or fries.

In the film The Martian, Matt Damon’s character, Mark Watney, is stranded on the red planet with nothing to eat but spuds. This is because potatoes have just about all the vitamins and minerals the human body needs to survive.

They are also wonderfully filling.
Of course, nobody food provides everything the physical body needs. The potato isn't a very good source of protein, which is where the bacon and soured cream are available .
Bacon gives us the fat and protein we'd like , as does soured cream , which also has a further boost of calcium, and other minerals and vitamins.
A potato with bacon and soured cream is a superb source of carbs, the body’s main source of energy.
If I were forced to survive on one dish it might be a loaded potato .