Preheat the Oven: Preheat your oven to 400°F (200°C) with a rack positioned in the center. Grease a 9 x 13-inch baking dish with olive oil.
Prepare the Bell Peppers: Trim, deseed, and dice one of the bell peppers. Halve the remaining bell peppers lengthwise, keeping the stems intact as much as possible. Remove and discard the seeds and ribs.
Cook the Rice Mixture: Heat the oil in a large skillet over medium heat. Once the oil is hot, add the diced onion and cook, stirring occasionally, until softened, about 4 minutes. Add the rice and salt, and cook for another 3 minutes, stirring occasionally.
Add Ingredients: Stir in the vegetable broth, diced tomatoes, green onions, taco seasoning, and diced bell pepper. Bring the mixture to a boil, then reduce the heat, cover, and simmer until the rice is tender, about 25 minutes. Stir in the black beans and corn, cooking until the mixture is fully combined and warmed through.
Stuff the Peppers: Arrange the halved bell peppers in the prepared baking dish. Fill each pepper with the rice mixture, dividing it evenly among the peppers. Top each stuffed pepper with shredded pepper jack cheese.
Bake: Bake the stuffed peppers, uncovered, in the preheated oven until the cheese is bubbling and golden brown, about 40 minutes.
Garnish and Serve: Sprinkle the stuffed peppers with minced fresh cilantro, if desired, before serving. Enjoy!