Prepare the pork by combining oregano, paprika, and cumin and rub the roast with the seasoning blend.
In the slow cooker, add water, orange juice, lime juice, onion, garlic and bay leaves. Place the pork roast in the slow cooker and cook on high for 5 hours or on low for 7-9 hours.
While the pork is cooking, prepare your cilantro pineapple sauce. Add sour cream, mayonnaise, garlic, jalapeno, lime juice and pineapple juice to your blender. Pulse the blender to combine ingredients before finally adding the cilantro and blending until smooth.
Once the pork is cooked through, shred with a fork and serve onto tostadas. Top with grated red cabbage, queso fresco and the cilantro pineapple sauce.