In a large skillet or Dutch oven with a lid, heat 2 tablespoons oil over medium. Add half the red onion and half the jalapeño, along with the cumin, and cook until fragrant and softened, 3 to 5 minutes. Add the rice and beans (including the bean liquid). Fill the can with water and add that, too (1¾ cups). Season with 1 teaspoon salt. When boiling, cover, reduce heat to low and cook undisturbed until the rice is tender, 18 to 20 minutes.
Meanwhile, in a medium bowl, stir together the remaining half red onion, half jalapeño and 2 tablespoons oil; the corn; cilantro; and juice from the lime. Season to taste with salt.
When the rice is ready, turn off the heat and sprinkle with cheese. Cover and let rest for 4 minutes. Spoon the rice and beans into bowls. Quarter the avocado and add a piece to each bowl, then top with the corn salsa and a few leaves of cilantro.
