If using, prepare the pork shoulder ragu.
For the baked mezzi rigatoni, preheat the oven to 375°. In a large, deep pan, heat the olive oil. Add all of the chopped vegetables and cook over moderate heat, stirring occasionally, until lightly browned and cooked, about 5-7 minutes. Season with salt and pepper.
Meanwhile, in a pot of salted boiling water, cook the pasta until al dente. Drain completely and cool under running water.
After the pasta has cooled a bit, put it back into the same empty pot (trying to save some dishes here), and add the pork shoulder ragu, all of the cooked vegetables, additional marinara sauce, 1 cup of mozzarella cheese and the sour cream. Mix thoroughly.
Pour all of your pasta mixture into a casserole dish and sprinkle with the remaining mozzarella cheese if desired.
Bake the pasta for about 30-35 minutes, or until golden. Let rest for at least 15 minutes. Sprinkle fresh parsley and freshly grated Parmigiano-Reggiano and serve.