The gluten-free bandwagon is becoming a little cramped these days. Pizza Hut offers an alternative pizza crust in 2,400 of its stores; the Girl Scouts introduced a gluten-free peanut butter oatmeal cookie; and this July General Mills is launching five of its best-known cereals in g-free versions. If ever there were a bellwether that gluten-free has become mainstream, it’s Cheerios. But thanks to an ingenious method of harnessing the power of gourmet mushrooms, we may once again be able to embrace that problematic ingredient: wheat.