Put the cheeks in a glass or ceramic dish, toss them in the marinade, cover and refrigerate overnight.
The following day, take the cheeks out of the fridge two hours before cooking to allow them to come to room temperature.
Preheat the oven to 140°C.
Heat the olive oil in a casserole dish. Remove the cheeks from the marinade and sear them over a medium-high heat. Take them out of the dish and set them aside.
Add the sliced onion, sliced capsicum and reserved marinade and cook over a medium heat until the vegtables are soft, about 5 minutes. Add a little of the stock and rub the bottom of the casserole dish with a wooden spoon to remove any stuck bits.
Return the cheeks to the casserole dish, add the remaining stock, bring to the boil, then cover with a lid and transfer to the oven.
Cook the cheeks for 4 hours. By this time, the meat will be very soft. Remove the meat, and shred it with a knife and fork before returning to the pot.
Serve the beef cheeks on warmed corn tortillas with a squeeze of lime juice and coriander leaves.