In a small bowl mix together the salt, pepper, cumin, oregano, and chili powder and mix until combined.
Pat the pork roast dry with paper towels and sprinkle the spice mixture over the top and rub it all over the roast.
Place sliced onion and minced garlic in the bottom of a slow cooker, then the chipotles, orange juice, and coca cola, and place the pork roast on top.
Cook on high for 5-6 hours or low for 8-10 hours
Shred pork with 2 forks. Place shredded pork onto a baking sheet and pour about 1/2 cup of the juices in with the meat. Place under broiler for 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.