Combine the rice, 2 cups of water, and salt in a saucepan. Bring to a boil, cover, and simmer for 15 minutes. Remove from heat and let sit 5 minutes. Fluff, then stir in lime juice and cilantro.

Heat olive oil in a skillet over medium heat. Cook onion until soft, about 3 minutes. Add garlic, cumin, and chili powder, cooking 30 seconds. Stir in black beans and ¼ cup water. Simmer until saucy, 5 to 7 minutes. Season with salt.

Heat a dry skillet over high heat. Add corn and cook without stirring until charred in spots, 3 to 4 minutes. Shake and cook 1 minute more. Transfer to a plate.

Divide rice among bowls. Top with beans, corn, avocado, a dollop of sour cream, and salsa. Finish with cilantro and a squeeze of lime. Serve right away.