If they knew of issues that could cause harm to their customers, then they certainly should be punished. This should include criminal charges, civil suits, and shutting down their business. They are clearly not interested in ethical issues, and shouldn't be allowed to stay open and make the same mistakes again.
I definitely think that Lidl's neglect to immediately warn the public about the paint thinner in its gravy provides grounds for a law. While I understand there may be a certain protocol the company has to follow in these types of events, withholding information from the public that could put people's health at risk is simply unacceptable.
Anyone that was injured in that two weeks that the company did not take action would have grounds to sue the company. The company could have warned people sooner. Instead, they decided to sit back and think about how public relations would deal with it. They didn't put the public first.
If the company knew and didn't immediately disclose that there could be toxic paint thinner in gravy, then there may be ground for a lawsuit. I'd imagine that one would have to prove that the company knew the paint thinner could cause harm, and demonstrate when it knew, and also that it waited to alert the public.