Freshly ground black pepper and kosher salt to taste
Preheat oven to 350 degrees F. Prepare a 9x9-inch casserole dish with nonstick cooking spray.
Heat olive oil in a large nonstick skillet over medium-high heat.
Add the sausage to the preheated pan and sauté for 4 minutes until the sausage is just brown. Add the diced onions and cook for an additional 4 minutes until the onions are fragrant and the sausage is cooked through.
Stir in marinara sauce and spinach and simmer uncovered on medium-low heat for 4 to 6 minutes, stirring occasionally.
Once the spinach has wilted, stir in beans, orzo and a pinch of salt and pepper. Turn off the heat while you prepare the peppers.
Cut off the top 1/2 inch of each pepper and remove the ribs and seeds. Place hollowed out peppers into the prepared baking dish and drizzle with olive oil and a pinch of salt and pepper.
Fill each pepper with sausage mixture and top with a layer of mozzarella. Sprinkle each pepper with Parmesan cheese and Italian seasoning, and cover with aluminum foil.
Bake the peppers for 30 minutes, then remove the foil and bake until peppers are tender and cheese is bubbling, about 10 to 15 minutes.
Freeze the baked and cooled peppers for a make-ahead meal!