Roast 3 medium/large bell pepper over an open fire (optional).
Place fire roasted peppers in a large bowl and cover with foil. Cool.
Once cooled enough to handle, remove the charred skin from the fire-roasted peppers.
Chop all the peppers (fire roasted and raw) into bite-sized pieces, removing the ribs and seeds and add them to a large bowl along with the chopped onions. Set aside.
Meanwhile, in a large Dutch (oven or heavy bottom stockpot), heat the oil over medium/high heat and partially brown the ground beef, breaking it up and stirring as it browns (about 7 minutes).
Add the chopped peppers and onions to the browning ground beef and cook, stirring occasionally for about 10 minutes for the ground beef to fully cook, and the vegetables to soften.
Add the brown rice to the pot along with the beef stock. Stir well.
Add 1 teaspoon additional salt, ½ teaspoon black pepper, garlic powder, cayenne pepper, smoked paprika, chili powder, and ground cumin into the stew and stir well to combine.
Reduce the heat to medium, cover and simmer for 30-40 minutes minutes.
Uncover and continue to simmer and stir occasionally (about 20 minutes) until the rice is tender.
Add the butter and apple cider vinegar to the pot right before serving, and check the stew for additional seasonings (salt and pepper), if desired.