For the Pulled Pork:
Preheat the oven to 160 degrees C.
Trim the pork shoulder of skin and any thick layers of fat.
Combine the brown sugar, cumin, paprika and salt in a small bowl and rub the pork all over with the spice mixture.
Allow the pork shoulder to stand for about 30 minutes.
Heat the olive oil in a large oven proof dish with a lid over medium-high heat and brown the shoulder on all sides for about 3 minutes per side.
Remove and add the dressing and beer to the pot and bring to a simmer, scraping the bottom of the pot with a wooden spoon to loosen any bits stuck to the bottom.
Return the pork to the pot, cover with the lid and place in the oven for 4 hours until the meat is tender and pulls away from the bone easily.
Shred the pork in the pot, using two forks to separate the meat and discard the bone.
Spoon some of the liquid over the pork to moisten the meat.
For the Nachos:
Preheat oven to 200 degrees C.
Peel and stone the avocado and mash roughly with a fork.
Mix in the lemon juice, season to taste and set aside.
Finely dice the tomato, chop the spring onion and mix together with a teaspoon red wine vinegar and season to taste with sugar, salt and black pepper.
Use a cast-iron pan or other oven-safe dish and layer the nacho chips first, then the pork and the top with the grated cheese.
Repeat once more and bake for 10 minutes until the cheese has melted and starts to bubble.
Dot the nachos with some of the sour cream, tomato salsa and torn coriander.
Serve immediately with the mashed avocado and rest of the sour cream and salsa.
There will be quite a bit of pork leftover. Freeze to use for another meal.