Rainbow Bundt Cakey

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

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.

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.

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

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

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.