Wash, dry and core/seed the peppers. Lightly brush the insides and outsides with some olive oil then sprinkle with a pinch of salt and pepper, place in a baking dish and set aside.
Brown the meat in a large non-stick skillet over medium heat. Use some oil to keep it from sticking (like I didn't). Drain, if needed, transfer to a bowl and set aside.
To the same skillet, add the onions and olive oil and sauté, stirring constantly, for 1 minute.
Add the mushrooms and sauté, stirring occasionally, until both the mushrooms and onions are soft and mostly cooked through.
Add the garlic and stir until combined and fragrant, about 30 seconds.
Add half the green onions and stir an additional minute.
Add the cooked sausage meat back to the skillet along with the parmesan cheese, all the spices and 1/4 cup of chopped fresh parsley. Stir until combined.
Add the worcestershire sauce and spinach.
Cook for a few minutes until the spinach is wilted through and nicely combined into the filling. Remove the skillet from the heat.
Add the shredded mozzarella and stir until well combined. We're ready to fill our peppers!
One by one, first using a spoon and then your hands to push down, really fill each individual pepper to the brim with the filling. Make sure you get the corners and crevices (using your fingers is key for this). The filling could be somewhat overflowing but keep a little bit of room to add some extra shredded mozzarella cheese.
Top each pepper with a nice helping of the remaining mozzarella cheese.
Cover with aluminum foil. PRO TIP:Partially stick a toothpick into the center of each pepper to ensure the foil doesn't come into direct contact with the cheese. Bake until peppers are tender, about 35 minutes. Uncover and bake until cheese is bubbly, about 10 more minutes. If you want the cheese more crispy and golden, broil on high for the last 5 minutes. Pay attention to it though, you don't want it to burn and ruin it in the final minutes of cooking. Garnish with the remainder of the green onions and parsley and serve.
Notes
Any ground protein can be used instead of Italian sausage. Ground beef, pork, turkey, chicken, lamb, bison, veal. You can even use crumbled tofu.