George Tenedios, the owner of Fresh&Co, a small New York chain of fast-casual restaurants, is constantly on the hunt for new ingredients. He’s experimented with all sorts of odd meat substitutes, from homemade tempeh to Silicon Valley darling Beyond Meat. But even he was stumped by a photo of what appeared to be a tuna sushi roll—shiny, bright-red "meat" with sesame seeds dotting the top—but which he knew was made not from any fish but from tomatoes.