Step 1

Preheat the oven to 375 degrees F (190 degrees C).

Step 2

Bring rice and water to a boil in a saucepan over high heat. Reduce heat to medium-low, cover, and simmer until the rice is tender, and the liquid has been absorbed, 20 to 25 minutes. Set the cooked rice aside.

Step 3

Cook onion and olive oil over medium heat until onion begins to soften, about 5 minutes. Transfer half of cooked onion to a large bowl and set aside.

Step 4

Stir marinara sauce, beef broth, balsamic vinegar, and red pepper flakes into the skillet; cook and stir for 1 minute.

Step 5

Pour sauce mixture into a 9x13-inch baking dish and set aside.

Step 6

Combine ground beef, Italian sausage, diced tomatoes, Italian parsley, garlic, salt, black pepper, and cayenne pepper into bowl with reserved onions; mix well. Stir in cooked rice and Parmigiano Reggiano. Stuff green bell peppers with beef and sausage mixture.

Step 7

Place stuffed green bell pepper halves in the baking dish over tomato sauce; sprinkle with remaining Parmigiano-Reggiano, cover baking dish with aluminum foil, and bake in the preheated oven for 45 minutes.

Step 8

Remove aluminum foil and bake until the meat is no longer pink, the green peppers are tender and the cheese is browned on top, an addition 20 to 25 minutes.