Preheat the oven to 400°F (200°C). Lightly coat a baking dish with cooking spray or a drizzle of olive oil and set it aside.

In a large skillet over medium-high heat, add the Italian sausage. Use a wooden spoon or potato masher to break it into small crumbles as it browns. Allow the sausage to cook until it begins to render its fat and develop color.

Add the diced onion to the pan and sauté for 4–6 minutes, stirring occasionally, until the onion becomes translucent and the sausage is fully cooked through. Stir in the minced garlic and cook for an additional minute until fragrant.

Pour in the marinara sauce (or crushed tomatoes) and ¾ cup of the stock. Stir to combine, then bring the mixture to a gentle simmer. Let it bubble for about 5 minutes, allowing the liquid to reduce slightly and the flavors to meld. Stir in the fresh basil.

Add the pre-cooked rice to the skillet and mix until everything is well incorporated. Stir in the mozzarella cheese and cayenne pepper, blending until evenly distributed. Taste the filling and season with salt if needed.

Using a small spoon or cookie scoop, generously fill each prepared cubanelle pepper with the sausage mixture, pressing lightly to pack the filling inside. Arrange the stuffed peppers on their sides in the prepared baking dish. Pour the remaining ¼ cup of stock into the bottom of the dish to help steam and soften the peppers during baking.

Cover the dish tightly with aluminum foil and bake for 40–45 minutes, or until the peppers are tender and the filling is heated through. Remove from the oven and let rest for a few minutes before serving.

Serve warm, spooning a bit of the pan juices over the top for added moisture and flavor. Each bite offers a perfect balance of smoky sausage, tender rice, and sweet pepper—comforting and flavorful from start to finish.