Season pork shoulder with Oaxacan Adobo, rubbing in thoroughly on all sides.
Place garlic, onions, orange juice, lime juice and seasoned pork shoulder into a slow cooker. Cover and cook on low heat for 8 hours or high for 4-5 hours.
Remove pork shoulder from the slow cooker and shred the meat before returning to the pot with the juices; season with salt and pepper, to taste, if needed. Cover and keep warm for an additional 30 minutes.
Preheat oven to broil. Place carnitas onto a baking sheet and broil until crisp and crusted, about 3-4 minutes.
Dice tomatos, avocados, sweet onion and jalapeno and put in a medium sized bowl. Roughly chop cilantro and add to bowl. Salt and pepper to taste. Mix well. Serve on pork taco