Salt and pepper pork liberally. Combine the oregano and the cumin with olive oil and rub all over pork. Place the pork in a slow cooker and top with the onion, garlic, and jalapeno. Squeeze the orange over the pork (removing any seeds) and place the orange half in the slow cooker with the pork. Cover and cook on low for 6-8 hours or on high 3-4 hours.
Once the meat is tender, remove from slow cooker and let cool slightly before pulling apart with a fork. In a large saute pan, heat the canola oil over high heat. Press the shredded pork into the oil and fry until crusty on one side, cover and set aside.
In the meantime, preheat oven to 425-degrees. Cover a cookie sheet with aluminum foil and place tortillas on top. Brush each tortilla with oil on both sides and bake for 5 min on one side. Flip tortillas over and bake an additional 2-3 minutes or until tortillas become crispy.
Place about 1/4 c. of the pork mixture on each tostada (you will have leftover pork... heats up great for leftovers). Top with lettuce and additional toppings and serve!