Even if you are right, and the only way for people to learn about slow cookers is by banning McDonalds / Chinese take out, I still wouldn't do it.
Although the slow cooker is a pretty good idea.
Once that is done, I would take items that are known health hazards and classifying them as toxic for consumption such as HFCs and hydrogenated oils. They are basically slow acting poisons. You would still be able to buy them and use them in your own home as an individual citizen, but food companies cannot buy them and use them to make food. Instead they need to use the healthier alternatives by default. This way all the junk food we enjoy today would still exist, but we would mitigate how unhealthy they are for us, since food companies would have to use the least unhealthy recipe possible.
I see this as reasonable since it preserves individual freedom, but prevents corporations, which have a fiduciary duty to psychopathy, from producing maximally unhealthy foods in search of a profit.
If those least unhealthy options were still economically attractive to the poor after the elimination of food subsidies and classification of cheaper, less healthy substances as unfit as an ingredient in manufactured foods, I would then look into how to incent people to choosing the healthier alternatives.
I think the best option here would be to make it easy for a family to acquire a cheap slow cooker and recipes and subsidize a ready-made pack of food that contains spices and other bulk ingredients used in the slow cooker recipes. The latter option is already done in Brazil under the name "cesta basica". Here's an image of the foods included in the "cesta basica"
http://www.utahpreppers.com/wp-content/uploads/2008/12/cesta...
You can feed an entire very well for very cheap on it. It's also available to everyone regardless of income.
You can go well beyond a slow cooker in time and money with a one time purchase of a solid pressure cooker. I have a 21-qt All American that I can produce tasty brown and black bean based meals at less than the cost of the Mac-n-Cheese. I'd cook about 15 quarts of beans in one evening, freeze 12 and eat the other 3 over the next few days.
If you were to ban ready-to-eat foods high in sugar and hydrogenated fats, you'd force people to learn about these alternatives. The benefit of banning is that it eliminates the path of least resistance where people remain ignorant of alternatives.
If people still want sweet foods and other things that are bad for them, they can still have them, but they have to do some work by cooking those sweet things themselves.