Preheat oven to 350° F.
Place halved jalapenos on a rimmed sheet pan. Line the pan with aluminum foil first, for easy clean up, if desired. Roast for 10 minutes, or until nicely softened. Remove from oven and let cool.
Heat a medium skillet over medium-high heat. Add oil. Once oil is warmed, add sausage and cook for 5 to 7 minutes, breaking it up occasionally. Add onion, pepper, and garlic, and cook for 5 minutes to soften. Once sausage is thoroughly browned, remove the mixture to a large bowl. Cool to room temperature (place in refrigerator to speed up cooling, if desired).
Add cream cheese and Parmesan to cooled sausage mixture. Fold thoroughly and then season with salt and pepper, to taste.
Place about 1 heaping tablespoon (depending on the size of your jalapenos) of mixture into each jalapeno half, and top with a bit of mozzarella cheese. Repeat until all halves are stuffed.
Place pan of stuffed jalapenos under broiler, and cook until mozzarella cheese is melty and blistered/browned. Remove pan from oven, sprinkle with a bit more shredded Parmesan, and then some fresh Italian parsley and/or chives. Serve hot or warm.
