Mix dry rub together excluding avocado oil. Pat pork butt dry and cut into 2-3 smaller pieces. Massage rub into pork butt.
Set Instant Pot on sauté mode. Once it's hot add avocado oil and sear pork butt pieces for 4 minutes per side. To ensure a good sear, avoid over crowding the pot and sear in 2 batches.
Place seared pork on baking sheet and set aside. Add onions, jalapeño peppers and garlic to Instant Pot and sauté for 4 minutes, stirring constantly.
Deglaze pot with lime juice and orange juice. Scrape the cooked bits off the bottom of the pot.
Return pork and any juices in the pan to Instant Pot. Close and pressure cook on high for 1 hour.
Meanwhile, make slasa fresca. Mix all ingredients together and refrigerate.
Preheat oven to 400℉.
Once pork has finished pressure cooking, vent Instant Pot. Be careful that steam is hot! Open lid only when all steam has been released.
Remove pork butt from Instant Pot with a strainer, reserve the liquid. Place pork on a baking sheet and shred with 2 forks. Place in oven for 10 minutes or until crispy. This step can be omitted if you don't want the carnitas crispy.
After removing from the oven (or after shredding if you choose not to skip the oven) toss pork with a ½ cup of reserved liquid. Freeze any extra liquid and use it the next time you braise a pork butt.
Serve carnitas on top of lettuce leaf with avocado and salsa fresca. For some added deliciousness add a dollop of sour cream or crumbled cotija cheese!