Heat the oil in a large nonstick or enameled cast iron skillet over medium-high heat.
Add the onion, reduce the heat to medium-low, and cook for 4-5 minutes or until it begins to soften.
Add the red bell pepper and beef. Cook for 5-6 minutes, breaking it up with a wooden spoon as it browns until it's no longer pink. Drain off any excess grease if necessary.
Add the zucchini and garlic and stir to distribute it evenly in the skillet.
Add the beef broth, salsa, chili powder, rice, and salt. Bring to a boil, reduce heat to low, cover, and simmer for 15-18 minutes.
Turn off the heat and let stand for 5 minutes or until the rice is fully cooked.
Add 1 cup of the cheese and stir until melted. Taste for seasoning and add more salt to taste and black pepper to taste.
Sprinkle with the remaining cheese and serve.