Maybe you know this phrase "to see sth. through rose-coloured glasses" This means a happy or positive attitude that fails to notice negative things, leading to a view of life that is not realistic. So I think this will fit perfect to the task. Lidl and Aldi show their customers not the realistic. They show things through the rose-colored glasses. You can use this keyvisual as Illustration or as real Image (Photo Collage with Stock photos). It is also good for guerilla street campaigns.
You can make posters & animated gifs with the glasses effect. And augmented reality glasses to show the suffering. And you can print pink and green paper-glasses (solar eclipse) or made with LED lights. And XXL glasses to put it over the Lidl and Aldi signet. The idea behind is easy to understand.