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.