Cook the brown rice according to the package instructions, about 40-45 minutes.
In a large skillet, heat olive oil over medium heat. Add the diced onion and bell pepper, and sauté until they are soft, about 5-7 minutes.
Add minced garlic, chili powder, and cumin to the skillet. Cook for another minute until fragrant.
Stir in the diced sweet potatoes and cook for about 10 minutes, stirring occasionally, until just tender.
Add the black beans, cooked brown rice, salt, and pepper to the skillet. Mix well and let everything heat through, about 5-7 minutes.
Remove from heat and garnish with fresh cilantro, if desired.