Heat the oil in a medium-size heavy skillet over medium-high heat. Add the onion, and saute for 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. Transfer the rice to a 7 by 10-inch flameproof baking dish. Drizzle with the creama or 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.
Remove from the oven and serve.
*Cooks Note: To char the chiles (or any fresh chile): Put the chiles over a gas flame or underneath the broiler and cook until they are blackened on all sides. Enclose them in a plastic bag and let stand for 10 minutes to steam, which will make them easier to peel. Peel, stem, and seed the chiles. Once peeled, the chiles may be chopped, sliced or stuffed.