How to Make It
In a large saucepan, combine the black beans, garlic and enough water to cover by 3 inches. Bring to a boil and simmer over moderate heat, adding more water as necessary, until the beans are tender, about 1 hour. Drain.
Meanwhile, in a medium saucepan, combine the rice and 1 3/4 cups of water and bring to a boil. Cover and simmer gently over moderately low heat until the water has been absorbed and the rice is tender, about 20 minutes. Transfer the rice to a rimmed baking sheet and refrigerate until cool. (You should have about 4 cups of rice.)
In a large skillet, heat 1/2 cup of the oil. Add the onion and cook, stirring occasionally, until golden, about 5 minutes. Using a slotted spoon, transfer the onion to a small bowl. Add 3 cups of the beans to the skillet and cook over moderately high heat, stirring frequently, until crispy, about 20 minutes. Stir in another 2 cups of the beans, the cooled rice, the sautéed onion and the remaining 2 tablespoons of oil. Stir to incorporate and season with salt. (Reserve the remaining 1 cup of beans for another use.) Transfer the beans and rice to a serving bowl and garnish with cilantro. Serve with lime wedges and chopped red onion.