Place sliced onion and minced garlic in the bottom of a slow cooker. Place pork on top. Add in the orange juice, coke, chipotle, and seasonings. Cook on high 5-6 hours or low 8-10 hours
Shred pork with 2 forks. Place shredded pork onto a baking sheet and pour about 1/2 cup of the juices over the top. Place under broiler 5-6 minutes, then toss and add another 1/2 cup juice and broil another 5 minutes.
Serve with warm tortillas, and a squeeze of lime. Garnish with cilantro, onions and cotija cheese.