Preheat and Prepare Peppers: Preheat your oven to 350°F (175°C). Rinse the bell peppers, then slice them in half horizontally. Use a paring knife to remove the stems and core from each half. Don’t worry if there’s a small hole left behind.
Roast the Peppers: Place all six pepper halves cut side up in a 9×13-inch casserole dish. Brush them with 1 tablespoon of oil and sprinkle with ¼ teaspoon salt and the black pepper. Roast for 20 minutes to slightly soften.
Cook the Filling: While the peppers are roasting, heat the remaining tablespoon of oil in a large skillet over medium heat. Add the sausage and cook until browned, breaking it up as it cooks.
Add Aromatics: Once the sausage is browned, stir in the diced onion and minced garlic. Cook until the onion becomes translucent and fragrant, about 3–4 minutes.
Simmer Rice Mixture: Stir in the uncooked rice, marinara sauce, Italian seasoning, garlic powder, 1 teaspoon salt, and chicken broth. Mix well. Cover the skillet and bring to a boil over medium-high heat.
Cook the Rice: Once boiling, reduce heat to low and let it simmer (covered and undisturbed) for 20 minutes. Then, turn off the heat and allow it to sit (still covered) for another 5 minutes.
Assemble the Peppers: Remove the lid, fluff the rice gently with a spoon, and stir to combine. Spoon the sausage and rice filling generously into each roasted pepper half.
Top and Bake: Sprinkle shredded mozzarella evenly over the top of each pepper. Cover the dish loosely with tented foil and bake for 15 minutes until heated through.
Broil to Finish: Remove the foil and switch the oven to broil. Broil for 2–3 minutes until the cheese is lightly golden. Keep an eye on it to prevent burning.
Garnish and Serve: Remove from oven, garnish with fresh parsley if desired, and serve warm.