In a mixing bowl combine the spice rub ingredients: 2 teaspoons oregano, 1 teaspoon cumin, 1 tablespoon adobo sauce, 2 teaspoons salt, freshly cracked pepper, and a dollop of olive oil.
Trim off any excess fat from the pork shoulder and chop it into large chunks, approximately 2-3 inches wide. Add to the mixing bowl and thoroughly rub the spices into the pork chunks.
Add the pork to the slow cooker, along with a roughly chopped onion, 4 peeled garlic cloves, and a jalapeno. Squeeze as much orange and lime juice into the slow cooker as you can. I add the leftover orange pieces to the slow cooker but this is optional.
Cook for 6-8 hours on low, or approximately 4 hours on high. When the meat pulls apart easily and is fully cooked on the inside it is done.
Remove any large veggie pieces and shred the pork pieces using two forks or a spatula. Taste for salt level and add additional salt if necessary (very important!). Let the shredded pieces cook for another 10-15 minutes in the slow cooker so the juices can infuse into the shredded meat.
To crisp up the carnitas, you can either cook them in a skillet over medium-high heat with a bit of oil until the juices evaporate and one side crisps up, or you can cook them under the broiler in the oven for 5 minutes or so.
To make pork carnitas tacos, warm up 12-16 corn tortillas. Each tortilla gets carnitas, Salsa Verde, finely chopped onion, cilantro, and a final squeeze of lime.
To make Salsa Verde, pull the husks off the tomatillos and give them a good rinse. Cut the stems out of the tomatillos. Roast the tomatillos in the oven for 10-15 minutes or until they start to turn army green. Add tomatillos to a blender along with 1/2 onion, 1 garlic clove, 10-15 sprigs cilantro, and 1/2 of the serrano pepper. Pulse blend and taste for heat level, adding more serrano if necessary.
Store leftover carnitas in their juices in an airtight container in the fridge.