Lawns were specifically invented to show off oneโs need not to grow anything on their land. Only the peasants were farmers. The upper class flaunted their wealth and status by planting lawns and ornamental gardens.
Not disputing that grass or communal grazing grounds existed, but the idea of having grass planted around your residence the way we do it today was a practice of elite medieval European landowners.
Soon, though, expansive lawns ensured that all could view European landowners' estates, explains Rooney. To use one's property for aesthetics and leisure, rather than food production, signaled vast amounts of wealth and financial security, says the Washington Post. Even the palace of Versailles boasted a lawn called a "tapis vert," which translates to a green carpet (via Scientific American).
So. If I'm every in a position where I can be an unethically constrained mad scientist type who really wants to make a difference...
I would engineer a virus, maybe delivered by mosquitoes, that inserts the ability to produce the enzyme cellulase into the human gut. This would allow us to eat grass in a pinch, likely solving world hunger. Of course, it would suck to eat grass, so most people wouldn't -- just like most avoid eating dandelions today. But it would be a cool fallback position in a global crisis.
There's a guy on youtube (The Thought Emporium) that did something similar so he could defeat lactose intolerance, however temporarily. For a while, until his gut shed its lining, he could synthesize lactase again. So doing the same with cellulase isn't that far fetched. What I would really be worried about is the prodigious amount of gas you would generate, as our guts aren't really mechanically built for that degree of rear-gut fermentation. I think you'd have to start with an elimination diet of some kind (keto?) and work forward to small amounts of vegetation to test what your body can handle. It's all doable, but risky.