Tinga is a traditional dish from the centre of Mexico. Flank steak and onion slices are simmered in a spicy tomato sauce with chipotle chillies until the beef is tender enough tot shred with a fork. It is usually served over corn tostadas covered with a thin layer of refried beans and topped with avocado slices.
Chipotle chillies in adobo are sold in tins so you can buy them in bulk. They are dried chipotle chillies in a sauce. They add heat and a smoked flavour to your Mexican dishes. They are available online and in Mexican grocers.