You can use the phrase pea soup to describe your lunch, but some people are just as likely to mean "a thick fog" when they talk about pea soup.
The literal meaning of pea soup is pretty obvious — it's a thick, savory soup, usually made from green or yellow split peas. The figurative meaning is less clear, since it means "a fog so thick you can't see through it." The first written mention of pea soup was actually spelled pease soup, in 1711. Londoners have been using it since at least the mid-1800's to describe their own famous fog.