Put the meat, fat side up, into a deep casserole dish or stainless steel pan. Tuck the garlic, onions and chillies around the meat.
Mix the tomato puree, spices and salt in a small bowl, then pour this around the meat, over the vegetables.
Put the dish into the oven and set to 120°C/250°F, combination steam setting. If your oven has variable steam settings, use 80%. If not, don't worry! Just set to combi steam at the correct temperature and the oven will figure out the humidity. There’s no need to preheat for this dish.
Cook until the meat is falling apart tender and the vegetables have broken down, about 3 ½ to 4 hours.
Let the cooked meat sit for 20 minutes, then shred with a couple of forks, discarding any large pieces of fat. Stir through the drained beans and serve as you like (suggestions above). Any leftovers will keep refrigerated for a couple of days or frozen up to 3 months.