Place pork roast in a slow cooker on medium heat and cook for 6-8 hours
When finished, reserve 1/2 cup of liquid from the slow cooker, shred the pork roast with forks, remove any excess fat, and return to slow cooker to sit in juices until ready. Set aside
Preheat oven to 400 degrees F.
Cut peppers in half lengthwise, remove seeds and stem and cut out any membranes. Set aside (optional: blanch for 5 minutes in a pot of boiling water)
In a large skillet over medium high heat, add olive oil, chopped onions, chopped mushrooms, and chopped zucchini. Sauté until vegetables are tender (about 5-10 minutes).
Chop tomatoes and green onions.
Combine vegetables, tomatoes, onions, and shredded pork meat to create stuffing mixture.
Place halved peppers into a baking dish.
Stuff with filling, dividing it equally between peppers.
Top liberally with mozzarella cheese
Add about 1/2 cup of the liquid from the slow cooker into the bottom of the baking dish. If you accidentally discarded it, just add stock or water.
Bake at 400 degrees F for 25 - 30 minutes, until peppers are tender, but not mushy.
Garnish with chopped cilantro and avocado, and serve immediately.