Preheat the Oven: Preheat your oven to 400°F (200°C) and grease a baking dish with olive oil.

Prepare the Peppers: Trim the tops off the bell peppers, remove seeds, half them lengthwise, and arrange cut-side up in the baking dish.

Sauté the Onions: Heat olive oil in a skillet, add chopped onion, and sauté for 4 minutes until soft.

Cook the Rice Mixture: Add rice and salt, pour in vegetable stock and diced tomatoes. Boil, then simmer covered for 25 minutes.

Add the Remaining Ingredients: Remove skillet from heat, fold in black beans, corn, and green onions.

Fill the Peppers: Fill each pepper half with the rice mixture and top with the shredded cheese.

Bake the Stuffed Peppers: Bake uncovered for approximately 40 minutes until peppers are tender and cheese is bubbly.

Garnish and Serve: Cool slightly, optionally sprinkle with cilantro, and serve warm.