Heat the oil in a medium-size heavy skillet over medium-high heat. Add the onion, and saute until translucent, about 5 minutes.
Add the rice and cook until the rice is opaque, about 10 minutes.
Stir in the water and the corn kernels, then season the water with salt and pepper, to taste. Bring the mixture to a boil. Reduce the heat to medium-low, cover, and simmer until the rice is tender, about for 15 minutes.
Preheat a broiler. Using a fork, fluff the rice and stir in the chopped poblanos.
5. Transfer the rice to a 7 by 10-inch baking dish. Drizzle with the sour cream and sprinkle the cheese over the top. Broil until the top is browned in spots and the cheese has melted, about 5 to 8 minutes.