Over medium heat, heat the olive oil in a large skillet. Once hot, add the beef and cook until little pink remains, breaking up with a wooden spoon, about 5 minutes.
To the skillet, add the onion and diced bell peppers. Cook until softened and beef is cooked through, about 5 minutes. Add the can of diced tomatoes, salsa, and brown rice; cook 1-2 minutes, stirring well to allow the rice to absorb the flavors. Add the beef stock, cumin, cayenne, chili powder, garlic powder, and smoked paprika; stir well.
Cover and cook 35-45 minutes, stirring every 5-10 minutes, until liquid is absorbed. Top with cheese and sliced green onions before serving.