Preheat the oven to 400 degrees F. Cut the tops off of the bell peppers and remove any seeds. Place peppers in a shallow baking dish with 1 inch of water. Cover with foil and bake for 20 minutes.
While bell peppers are baking, make the filling. Heat oil in a large skillet over medium heat. Add onions and cook until translucent. Crumble tempeh into small pieces and add to onions. Sauté until lightly browned, about 5 minutes. Stir in taco seasoning. Remove from heat and add cooked rice, black beans, corn, red onions, salsa, nutritional yeast, and lime juice. Season to taste.
When peppers are done, remove from oven and turn the oven down to 350 F. Drain water from the pan then evenly divide the filling between the 6 peppers. Cover in foil and bake for another 20 minutes.
While peppers are baking, combine the ingredients for the avocado creme in a food processor, mixing until smooth.
Remove peppers from the oven. Let cool 5 minutes then top with avocado creme and serve immediately.