Within our current political-economic system? End subsidies for farmed meat, subsidize alternatives, and raise awareness on the issue as well as about health effects of excess meat consumption.

This will have the "push" effect of driving up farmed meat prices while having the "pull" effects of cheaper, healthier alternatives. There is nothing in particular to enforce.

Edit: and as the market on farmed meat becomes less profitable producers will leave the industry as well which leads to a sort of "spiral" as scarcity goes up, raising prices, pushing more away.