Preheat oven to 350 degrees.
Remove tops from peppers and scrape out membranes and seeds. Set aside.
Melt butter in skillet over medium heat and add onions. Cook until soft, about 5 minutes. Add in garlic and cook for 1 additional minute.
Stir in black beans, cumin, chili powder, and garlic salt. Using the back of a fork, mash up about half of the black beans. Add in cilantro and salsa and cook for 2 more minutes. Remove from heat and stir in cooked rice.
Evenly fill the four prepared peppers with the rice and black bean mixture and set inside a baking dish. Top each pepper with a ¼ cup of cheese. Bake in preheated oven for 30-40 minutes until peppers have softened and cheese is melted. Enjoy!
