Depending on your situation, a big fuck off size pair of noise cancelling headphones (or if budget doesn't allow, just headphones that looks noise cancelling), and being as absorbed into your screen as possible usually works. When I eat lunch on my own, I sometimes even furiously type out a long winded rambling and incomprehensible email to myself to make it look like I'm super busy. The people who see eating by yourself as a bad or concerning thing usually don't see treating lunch as a work catch-up hour as a bad thing