Rinse the pork with cold water, then pat completely dry.
Season each surface with salt and pepper (1/4 tsp. of each per side).
Mix cumin, paprika, and oregano together in a small bowl. Divide in half, and sprinkle the top side of the pork loin with half of the mixture, evenly distributing it across the entire surface of the loin.
Slowly drizzle olive oil (about 1 tablespoon) onto the top side of the loin, patting gently so it sticks to the seasonings and the pork.
Flip the pork loin over and repeat on the other side.
Place the pork loin into your crockpot, and set the temperature to "low".
Add minced garlic, jalapeño and onion to the top of the pork loin.
Cut the orange in half, and squeeze the juice from each half directly on top of the pork loin and veggies. (Or pour orange juice directly onto the top of the veggies).
*optional* : also pour the beer on top of the veggies.
Cover and let it cook for 8 1/2 - 9 hours, or until tender enough to shred.
Remove crockpot lid, and shred the pork before removing it from the crockpot. I simply used tongs to do this (it should be VERY tender). Mix the shredded pork in with all of the juices in the crockpot, too.
Serve on warm tortillas, and top with pico de gallo or any garnish you prefer!