Rinse brown rice under cold water. Combine in a medium saucepan with vegetable broth, bringing to a gentle boil. Reduce heat, cover, and simmer for 40-45 minutes until tender. Fluff and set aside.

In a large skillet, heat olive oil over medium heat. Add chopped onion and minced garlic, sauté until fragrant and translucent, about 3-4 minutes. Add diced bell pepper and cook for another 4-5 minutes until softened.

In a large mixing bowl, combine cooked brown rice, drained black beans, canned tomatoes, and sautéed vegetables. Sprinkle cumin and chili powder, stirring gently to mix, keeping black beans intact.

Preheat your oven to 375°F (190°C). Grease a casserole dish with cooking spray. Pour in the rice and bean mixture, spreading evenly.

Cover the casserole with aluminum foil and bake for 45 minutes. Remove the foil and continue baking for another 15 minutes until the top is crispy and golden.

Remove from the oven and let rest for about 10 minutes before serving. Garnish with avocado or fresh cilantro if desired.