In a small bowl, combine chili powder, cumin, oregano and onion powder. Season pork shoulder pieces with salt and pepper and the spice mixture, rubbing in thoroughly on all sides.

Place seasoned pork shoulder pieces into the slow cooker. Pour the orange juice, lime juice over the top. 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 on a sheet pan with a fork. You can also use kitchen shears to cut into smaller pieces.

Pour the juices from the slow cooker through a strainer. Add the strained juices back into the pot of the slow cooker. Turn the slow cooker to the warm setting.

Preheat oven to broil. With the carnitas on a baking sheet and broil until crisp and edges crust a little, about 3-4 minutes.

For serving: add the shredded pork back into the juices in the slow cooker and cover.

Serve warm on tortillas with diced onions, thinly sliced radishes and sliced avocado or guacamole.