In a large pot place in the pork, onion, garlic, salt, chili powder, cumin and fill with water and place onto the stove and bring to a boil for 5 minutes and reduce heat to a low simmer for 2 1/2 hours or until the pork in tender. Remove the pork and set aside to cool to room temperature and pour the stock into a colander and trash the onion and garlic.
In a mixing bowl hand shredded Carnitas meat and the rest of the ingredients and combine and set aside for 15 minutes.
Slice the onion into 1/8” strip and place into a nonstick skillet with oil and sauté over a medium heat until light brown and tender. Combine the Carnitas mixture and onion and sauté until light and crispy.
In a medium size skillet lightly oil over a medium high heat, place a corn tortillas, slice of pepper jack and top with corn tortillas and when the pepper jack cheese slice start to go soft turn the corn tortillas over and when both side in a lightly brown and take some of the Carnitas filling and one half and fold in half and pan fry until light and crispy on both side. Repeat this step until done. Sprinkle both side of the taco with Parmesan cheese and serve warm.