Place the onion and pepper strips in a large pot over medium high heat, and saute until they start to thaw.
Add the garlic, cumin, and tomatoes, and cook until the mixture starts to get hot, about 5 minutes.
Mix in the rice and the broth and bring to a boil.
Reduce the heat to low, cover the pot, and simmer for 40 minutes or until the liquid is absorbed.
Stir in the black beans and the cilantro (if using).
Remove from the heat and let the mixture sit for a few minutes, then serve.