Heat 2 teaspoons olive oil in a large skillet over medium-high heat.
Add 1 tablespoon minced garlic, the minced small red onion, and the diced red and green bell peppers; sauté until tender, about 3–5 minutes.
Add 1 pound lean ground beef to the skillet and cook, breaking it up, until browned, about 7–10 minutes.
Stir in 3 tablespoons taco seasoning, 2/3 cup tomato sauce, 2 tablespoons green chiles, and the drained and rinsed can of black beans; cook for 2 minutes to combine flavors.
Add 1 cup quick-cooking brown rice and 1 1/2 cups beef broth; bring the mixture to a boil.
Reduce heat to low, cover, and simmer until the rice is tender and most liquid is absorbed, about 20 minutes.
Evenly sprinkle 2/3 cup shredded Mexican-style cheese over the skillet, cover until cheese melts, about 2–3 minutes; alternatively, place skillet in a preheated 400°F oven for a few minutes to melt.
Garnish with chopped fresh cilantro and diced avocado, then serve hot.