Heat the olive oil in a large saucepan over medium heat. Add the onion and cook until softened, about 5 minutes.
Add the garlic and cook for another minute, until fragrant.
Stir in the cumin, salt, and pepper, and cook for another minute.
Add the rice to the pan and stir to coat with the onion mixture.
Pour in the water and add the drained and rinsed black beans. Stir to combine.
Bring the mixture to a boil, then reduce heat to low, cover the saucepan with a lid and let it simmer for 18-20 minutes, or until the rice is tender and the water has been absorbed.
Once done, remove the saucepan from heat and let it sit for 5 minutes with the lid on.
Fluff the rice with a fork, then serve the rice and black bean mixture in bowls, garnished with fresh cilantro, if desired.