Cut the top off of each pepper and remove the seeds. Replace the tops of the peppers.
Fill a large stockpot with about an inch of water and place peppers upright in a steamer rack (if you don't have one, directly in the water is fine). Cover and steam for 8-10 minutes. Remove lid.
While the peppers are steaming, heat olive oil in a saucepan over medium heat. Add onions and jalapeno and cook until onion is slightly softened and transparent, about 5 minutes.
Add garlic, chili powder, cumin and oregano and cook for about a minute, stirring constantly.
Pour in rice and stir until coated. Add tomato sauce and water/stock and bring to a boil. Reduce heat to low, cover, and cook for 20 minutes.
Remove from heat and add black beans, corn, cilantro and cheese. Season with salt and pepper.
Fill peppers, cover each with the top of the pepper, and place back in the steaming pot. Steam for another 3-5 minutes until heated through.
Top with any garnishes - cheese, sour cream, avocado, or salsa - and serve.
Notes
I like my peppers to keep a little bit of crunch, so I tend toward the lower steaming times. If you prefer softer peppers, use the longer cooking times.
Recipe by Baked In at https://www.baked-in.com/2012/05/07/mexican-stuffed-peppers/