Cover the bottom of the slow cooker pot with the onions and garlic. Cut the pork into two equal-sized pieces and rub them all over with the spice blend. Place the pork on top of the onions and add 100ml cold water. Cover with a lid and cook on high power for 4 – 4.5 hours or on low power for 7.5 – 8 hours. (See below for an oven-cooked method.)
Thirty minutes before the end of the pork cooking time, pre-heat the oven to 200°C / 180°C fan / gas 6. Bake each tortilla on a baking tray for 8 minutes until crisp and golden brown – depending on the size of your oven you may need to do this in batches.
In a small bowl, prepare the salsa by combining the pineapple, red onion, chilli, and lime juice. Add 2 tablespoons of the coriander and stir through.
When the pork is done, remove it from the slow cooker and place it in a large bowl leaving the cooking liquid and onions behind. Shred using two forks, removing any large pieces of fat. Add some of the onions from the slow cooker if you like and a spoonful or two of the cooking liquid to taste.
To serve, arrange the lettuce leaves on the tortillas followed by the pork, some of the sour cream and then the pineapple salsa. Garnish with the remaining coriander.
Cook’s tip: if you don't have a slow cooker this dish works perfectly well in a casserole in the oven. Divide the meat into 4 pieces instead of 2 and add an extra 150ml cold water. Cover and cook at 150°C / 130°C fan / gas 2 for up to 4 hours, checking after 2.5 hours to see how tender it is – the meat should have no resistance when pierced with a fork and fall apart easily.