Burgers are having a moment in mainland China, with budget-conscious diners and smaller households turning the humble sandwich into one of the country’s hottest fast-food battlegrounds, drawing in everyone from global restaurant chains to hotpot operators and coffee brands. Yum China’s Pizza Hut Burger Bar format, in which a burger counter operates alongside an existing Pizza Hut restaurant, expanded to more than 200 outlets in six ‌months, the company said in July. It plans to grow to 500 to...