Preheat oven to 350°F.
Place halved peppers on a large rimmed pan, cut side up. Roast for 30 minutes, or just until nicely softened. Remove from oven. Leave oven at 350° F.
While peppers are roasting, cook mafalda pasta in salted water to just al dente. Drain and set aside.
Also, heat a large skillet over medium heat. Add sausage and let it brown, breaking it up into bite-size pieces with a spatula. When sausage is about half-way browned, add onion and garlic. Once sausage is browned and onion is softened, drain any excess oil from pan. Stir in marinara sauce, Italian herb mix, and 1/8 teaspoon of the black pepper. Fold in cooked pasta. Once thoroughly heated, turn off heat.
In a small bowl, combine ricotta cheese, grated Parmesan, kosher salt, and remaining ⅛ teaspoon black pepper.
Divide ricotta cheese mixture evenly into the bottoms of each of the roasted pepper halves, spreading just a bit. Top ricotta mixture with a layer of pasta/marinara mixture. Aim to use about half of the mixture, snuggling it into the nooks and crannies of the peppers. Then divide 4 ounces of the shredded mozzarella cheese over the top of the pasta/marinara mixture.
Divide remaining pasta/marina mixture over the mozzarella cheese. Top with remaining 2 cups of mozzarella, dividing evenly among all the pepper halves. Tent very loosely with a large piece of foil, taking care to not let the foil touch the cheese – this will help any exposed noodles to not get hard and crunchy.
Bake for 20 minutes. Remove foil and place baking sheet about 8″ under broiler and broil until cheese is bubbly and golden and a bit blistered.
Remove peppers from oven and let rest 5 minutes before serving. With a zester/grater, grate fresh Parmesan cheese over the top and sprinkle with chopped fresh parsley, if desired.