In a small bowl, whisk together cumin, chili powder, oregano, 1 1/2 teaspoons sea salt and pepper. Remove excess fat from pork and cut into slices. Toss in a large bowl with spice mixture. Set aside.
Juice one orange into the Instant Pot and add 1 teaspoon of orange zest as well. Mince garlic, add to pot. Slice half the onion, and finely dice the remaining half. Add slices to the Instant Pot. Add pork and lock the lid in place.
Set the Instant Pot to MANUAL for 1 hour, 15 minutes. Once it beeps use the QUICK RELEASE method to vent. Carefully open the lid and shred pork using 2 forks.
Add finely diced onion to a mixing bowl with pineapple (cut into chunks). Dice pepper and chop cilantro, add to mixing bowl. Juice 2 limes into the pineapple mixture; add oil and sea salt. Mix together to coat evenly.
To each tortilla, add spinach, pork and salsa. Serve with orange wedges on the side.