Combine the oregano, salt, paprika, garlic powder and chipolte powder together in a bowl. Rub spices all over pork. Wrap pork in plastic wrap and refrigerate for 8 hours or overnight.
The next day, remove plastic wrap, place pork in the slow cooker and cook on low for 8 hours.
Turn grill to medium heat. Place pineapple on grill and cook 2 - 3 minutes per side or until dark char marks appear. Remove from grill and allow to cool.
Once cool dice. Combine pineapple, cilantro, peppers, lime juice and lime zest together in a bowl. Cover and refrigerate for at least 30 minutes.
With pork still in slow cooker, use forks to shred. Cover and turn to warm setting while you fry the taco shells.
Heat a thin layer of oil in a skillet over medium-high heat. Fry one tortilla, 15 - 30 seconds on each side. Transfer to a paper towel lined plate. Repeat with remaining shells.
To make a taco, spoon shredded carnitas into a taco shell, top with a spoonful of salsa and sprinkle with crumbled cotija cheese. Serve.