Toast the pecans in a medium non-stick frying pan over medium heat, stirring often, until browned, about 4 minutes. Take care not to burn. Transfer to a plate.
Heat the vinegar, sugar and butter in the same pan over medium-low heat. Add the beetroot. Cook, stirring often, until beetroot is heated through and all the liquid is absorbed, about 5 minutes. Top with pecans. Serve at once.