In a large Dutch oven add the pork, garlic, salt and pepper, and water. Bring to a boil, then reduce heat, cover and simmer over medium low for 45 minutes to one hour.
Drain well.
When cool enough to handle, shred the meat by hand or with the tines of a fork.
Remove and discard any remaining fat.
Transfer back to Dutch oven and heat the olive oil.
Add the orange juice and milk and cook until liquid has evaporated and pork has browned; stirring occasionally. Season with salt and pepper to taste.
Chop onions and cilantro, and slice avocado and limes.
Place each in small individual bowls for serving.
Heat tortillas in a dry frying pan and keep warm.
For each taco, stack 2 tortillas and layer with warm carnitas, chopped cilantro, onion and avocado slices and give it a good squeeze of lemon juice.
