Combine the spices with the oil in a bowl and mix into paste.
Cover the pork tenderloin with the paste, rubbing it in and making sure it is completely covered.
Place the meat into your slow cooker.
Top with the onions and jalapeños.
Add the cup of orange juice. Squeeze the juice from the lime and toss in the rind.
Set the slow cooker to low and cook for about 8 hours.
When done, remove the pork and set on a cutting board. Remove lime rind from the juices left in slow cooker.
Using two forks, shred the meat.
Place the meat back in the slow cooker with the juices.
Let everyone serve themselves from the slow cooker. Have a stack of just prepared corn tortillas, sliced red onion, tomato, or your favorite toppings.