Prepare the Peppers. Start by washing the bell peppers and cutting off the tops. Carefully remove the seeds and membranes from inside the peppers, creating a hollow space for the filling. Rinse them again to ensure no seeds remain.
Sauté the Aromatics. Set your Instant Pot to "Sauté" mode and heat the olive oil. Add the diced onion and minced garlic, sautéing until they turn translucent and fragrant.
Brown the Meat. Add the ground beef or turkey to the Instant Pot, breaking it apart with a spatula. Cook until the meat is no longer pink and is nicely browned. If you're using a meat substitute, follow the instructions on the package for cooking.
Season the Filling. Add the cooked rice, black beans, corn, diced tomatoes, ground cumin, chili powder, paprika, dried oregano, salt, and pepper to the Instant Pot. Stir everything together and let it cook.
Stuff the Peppers. Fill each hollowed-out bell pepper with the mixture from the Instant Pot. Press the filling gently to ensure it's packed well.
Pressure Cook. Pour one cup of water into the Instant Pot. Place the trivet inside and carefully arrange the stuffed peppers on top. Close the lid, set the valve to "Sealing," and select the "Pressure Cook" or "Manual" mode. Cook on high pressure for about 8 minutes.
Quick Release and Add Cheese. Once the cooking time is up, quickly release the pressure. Open the Instant Pot, and sprinkle the shredded Mexican cheese over the stuffed peppers. Close the lid and let the cheese melt.
Serve and Garnish. Remove the stuffed peppers from the Instant Pot. Garnish with chopped cilantro and serve!