She studied at Street Paul"s Girls" School and Ballymaloe Cookery School and worked as a freelance cook and writer, with influences from time spent in Mexico.
She has made two series of cookery programmes for Channel 4 with co-presenter Guy Grieve: Wild Gourmets in 2007 and A Cook"s Tour of Spain in 2008. In 2011, she presented Mexican Food Made Simple for Channel 5. She is co-editor with Annabel Buckingham of the cookbook Soup Kitchen (with an introduction by Hugh Fearnley-Whittingstall).
She has also written Cook: Smart Seasonal Recipes for Hungry People, The Wild Gourmets: Adventures in Food and Freedom, with Guy Grieve, and Mexican Food Made Simple.
Miers opened the first of her own restaurants, Wahaca, in the West End of London in August 2007, focused on Mexican street foods. In October 2008 a second Wahaca opened at Westfield in London.
Since then she has opened two further restaurants in Canary Wharf and Soho and in 2011, Wahaca launched their first mobile street kitchen, selling Mexican street food on the streets of London. As of September 2015, Wahaca had 19 branches.